THE SOCIAL LIFE OF ANIMALS
THE
SOCIAL
LIFE
OF ANIMALS
BY W. C. ALLEE
PROFESSOR OF ZOOLOGY
THE UNIVERSITY OF CHICAGO
WW- NORTON & COMPANY • INC
Publishers, New York
Copyright, 1938, by
W. W. Norton & Company, Inc.
70 Fifth Avenue, New York City
First Edition
Published by arrangement with
The University of Chicago Press
printed in the united states of AMERICA
This hook is gratefully dedicated to the past and present
members of our "Ecology Group"; without their enthusi-
astic co-operation much of the underlying evidence could
not have been collected during my lifetime, and without
their critical attention the expression of these ideas
would have been more faulty.
Contents
Foreword 13
I. Science versus Metaphysics 15
II. History and Natural History 20
III. Beginnings of Co-operation 50
IV. Aggregations of Higher Animals 90
V. Group Behavior 133
VI. Group Organization 175
VII. Some Human Implications 209
VIII. Social Transitions 244
Literature Cited 277
Index 289
52556
Illustrations
PLATES
FACING PAGE
I A. A hibernating aggregation of ladybird beetles 32
I B. A breeding aggregation of midges 32
II. A grassland-bison community 38
III. Aggregating behavior of brittle starfish 44
IV. Diagrams showing the effect of population size
on the rate of evolution 128
V. Castes of a termite from British Guiana 266
FIGURES
PAGE
1. Grasshopper nymphs on the march 36
2. The effect of numbers present on rate of bio-
logical processes 52
3. Group protection from ultra-violet radiation
for planarian worms 60
4. Another aspect of group protection for plana-
rians 62
5. The small marine flatworm Procerodes 64
6. Group protection from fresh water for Proce-
rodes 66
7. Bacteria frequently do not grow if inoculated
in small numbers 67
8. The common sea-urchin Arbacia 70
9. Arbacia eggs cleave more rapidly in dense
populations 72
10. Robertson found that two protozoans placed
together divided faster than if isolated 76
9
lO ILLUSTRATIONS
PAGE
11. Other protozoa reproduce more rapidly when a
certain number of bacteria are present 78
12. Some protozoans divide more rapidly in dense
bacterial suspensions if more than one is
present 79
13. A and B. A recent suggestion concerning the
ancestral relations within the animal king-
dom 86
14. Goldfish grow more rapidly if placed in slightly
contaminated water 95
15. An extract from the skin of goldfish frequently
has growth-promoting power 97
16. White mice grow faster in small groups than in
large ones 101
17. Flour beetles reproduce more rapidly if more
than one pair is present 105
18. The "spread" of time in which eggs are laid in
a colony of herring gulls affects the per-
centage that survive ii2
19. In small populations, genes drift into fixation
or loss largely irrespective of selection 121
20. In medium populations complete fixation or
loss is less likely to occur 123
21. In large populations, gene frequency is held to
a certain equilibrium value by the opposing
pressures of mutation and selection 124
22. As intensity of selection increases it becomes
more and more dominant in determining the
end result 126
23. Manakin males establish rows of mating courts
in the Panamanian rain-forest 134
24. Many kinds of fishes eat more if several are
present 136
ILLUSTRATIONS 1 1
PAGE
25. An ant which works at an intermediate rate
may be speeded up if placed with an ant
which works more rapidly, or vice versa 141
26. A simple maze used in training cockroaches 151
27. Isolated cockroaches make fewer errors during
training than if paired or if three are trained
together 152
28. They also take less time 153
29. Parrakeets learn equally well if trained when
isolated, whether they are caged singly or in
pairs 156
30. Parrakeets learn more rapidly if trained alone
than if two are placed together in the maze 157
31. Feeding a fish which has just come through the
opening from the larger side of the aquarium 160
32. Goldfish learn to swim a simple aquarium-maze
the more readily the more fish there are
present 161
33. Isolated goldfish learn the problem set for them
less rapidly, and unlearn it more readily 162
34. The aquarium-maze used in training part of
the fish to come forward and part to go to the
rear to be fed 164
35. Cyprinodon learn to move in a body more read-
ily than to split into two separate groups 165
36. Goldfish learn more readily if accompanied by
a trained leader 166
37. An aquarium-maze arranged to test the power
of observation of fish 168
38. Goldfish react more rapidly if allowed to watch
others perform ^ 169
39. Flocks of hens are organized into a definite so-
cial hierarchy 178
40. Cockerels also have a social organization 180
1 2 ILLUSTRATIONS
PAGE
41. In flocks of pigeons the organization is one of
peck-dominance rather than of peck-right 187
42. The Dionne quintuplets also show evidence of
a social organization among themselves 204
43. The percentage of births that were canceled by
deaths for the given years in Italy and Ger-
many 220
44. The percentage which deaths were of births
steadily increased during the war years 223
45. Crepidula fornicata shows sex reversal 254
46. Mated males of Crepidula fornicata retain that
stage longer 256
47. Castes of the common honey-bee 260
48. Some ant castes 265
49. The brown locust of South Africa has a swarm
phase which is distinct from the solitary
phase 273
Foreword
I WAS recently honored by an invitation to give the
Norman Wait Harris lectures at Northwestern Uni-
versity; the more so since as one of their side-door
neighbors I live close enough for my personal foibles
to be well known, thereby removing the chief source
of any possible glamour. In this book which grew out
of those lectures, as in the lecture series itself, I make
no effort to pose as the remote purveyor of a mys-
terious erudition; I could not in any case regard my-
self as more than the exponent of the glorified com-
mon sense which I more and more firmly believe all
science should be.
Even more than most, this book is the outgrowth
of years of co-operative effort. Some of the basic
facts were collected with the aid of funds from the
Rockefeller Foundation given to aid biological re-
search at the University of Chicago. Other researches
were supported directly by that university and more
recently by a grant for the study of the effect of
hormones on behavior from the National Research
Council.
13
x\^
1 4 FOREWORD
In addition to the personal aid received from my
scientific associates, many of whom will be named in
the text, the kindly criticism of Professor Alfred E.
Emerson has been particularly helpful in developing
the work and in shaping the content and implica-
tions of these lectures. My thanks are given also to
Professor Sewall Wright for his criticism of Chapter
IV, to Mr. Kenji Toda for preparing the illustra-
tions and to Marjorie Hill Allee, whose command of
the written word has been a constant resource.
W. C. Allee
The University of Chicago.
Mm Science versus Metaphysics
THE RATE of obsolescence of material things is
high. With consumers' goods we are well aware of
this fact; and even capital goods usually become out
of date in a long generation. Last summer an admirer
of Will Rogers dedicated a lasting monument to the
humorist. Although built for time and erected in our
semi-arid West where decay is slow, the tower is ex-
pected to last only a thousand years. Invested capital
evaporates even with watchful care; there are few
private collections of material wealth that remain in-
tact a third of a thousand years.
Oddly enough, the most permanent contributions
of our age appear to be the scientific discoveries we
have made, the artistic beauties we have created, and
the ideas we have evolved. To the extent that these
advances are entombed in libraries and museums
they share the impermanence of more material
things. A nearer approach to immortality is per-
mitted those bits of science and art that escape from
the bindings of books and pass into the active life
IS
l6 THE SOCIAL LIFE OF ANIMALS
and traditions of people. The more widespread and
firmly fixed these become in the minds of living men,
the greater is their chance of longevity.
The most practical achievement of our extremely
practical period is the habit of searching for new
truths and for correct interpretations of those long
known. The unique contribution of the present era
is not that made by men of business and affairs, spec-
tacular as it may be. Rather this age is and will
be known as the time of the development and ap-
plication of scientific methods. These contributions
are being made by extremely impractical research
workers who are supported by a tiny splinter from
the great block of capital gains. Money spent effec-
tively to this end, whether in the aid of research or
other creative scholarship, or in teaching the results
gained by research, makes the most lasting and im-
portant of all modern investments. The most nearly
permanent monument any man can erect is to have
influenced directly or indirectly the growth of im-
proved ideas and traditions among the men in the
street, in the factory or on the farm.
It is in this spirit that I have undertaken to inter-
pret one of the significant biological developments
of recent years. It is my hope that from the work
described in these pages, all social action may have a
somewhat broader and more intelligent foundation.
SCIENCE VERSUS METAPHYSICS 17
We can gain the impression from some modern
oversimplifications that science deals with empirical
facts, that philosophy attends to principles and
eternal truths, and that religion is concerned with
values. In the following pages it will be necessary
to shake aside such artificial limits and to present
principles along with the evidence that supports
them; to test these against experience and to attempt
frequently to weigh the general biological values
involved. This last process will be easier if we assay
survival values only. Admittedly in dealing even
with survival values we must be relatively rough
and ready in our methods, and perhaps the conclu-
sions will carry a strong odor of the laboratory in
which they had their origin.
Basically the approach will be that of the experi-
mental biologist rather than that of the theorist,
which might be more polished, or of the philoso-
pher, which would certainly be more abstract and
would probably use a great many more words for
the same number of ideas. Despite much practice
to the contrary, any biological fact which concerns
us can be accurately described and the conclusions
from its study be clearly expressed in relatively sim-
ple and direct language.
In research reports and scholarly discussions there
is need for the conciseness and precision made pos-
l8 THE SOCIAL LIFE OF ANIMALS
sible by technical language. Science has no need,
however, and is ill-served by any tendency to de-
velop a cult of obscurity. Scientists must be free to
attack the unknown as effectively as they can and
in return for intellectual freedom they have an
obligation, which rests heavily on those able to do
so, to interpret research results in terms which can
be understood by intelligent and interested people.
There is current in at least one American uni-
versity at present an attempt to organize all knowl-
edge about metaphysics, and so secure a longed-for
unity. In order to obtain a simplified system, the
group of men occupied with this enterprise turn
back to the days before the present scientific era to
find a statement of eternal principles which will
serve as a unifying nucleus for human experience
and thought. Such efforts at establishing a Neo-
Scholastic philosophy, while furnishing an excellent
corrective for overconfident scientists, seem mis-
chievously naive as a serious, present-day movement.
We do need relief from our absorbed attention to
conflicting scientific detail, but progress must needs
come from newer syntheses which take account of
the world and man as science sees them rather
than by accepting almost as a whole some ancient
system of historical significance. These systems are out
of date primarily because they were evolved before
SCIENCE VERSUS METAPHYSICS IQ
one of the greatest advances in knowledge that man
has yet been able to make, that of modern science.
Modern philosophical educational systems, if they
are to survive, must have as their central core the
well-tested evidence compiled by objective scientific
methods. Such knowledge must have stood the test
of being checked and re-checked by men constitu-
tionally agnostic in their mental attitudes; who can
say, "I don't know. What is the evidence?"; who are
constantly seeking critical new evidence concerning
the validity of their ideas.
An anecdote that is becoming classic among scien-
tists will illustrate the point. Professor Wood, phys-
icist of Johns Hopkins, was asked to respond to the
toast "Physics and Metaphysics" at a dinner of some
philosophical society. His response was somewhat as
follows:
The physicist gets an idea which seems to him to
be good. The more he mulls over it the better the
idea appears. He goes to the library and reads on
the subject and the more he reads the more truth
he can see in his idea. Finally he devises an experi-
mental test and goes to his laboratory to apply it.
As a result of long and careful experimental check-
ing he discards the idea as worthless. "Unfortu-
nately," Professor Wood is said to have concluded,
"the metaphysician has no laboratory."
History and Natural History
LIKE other human disciplines, science has its or-
thodox and its heterodox views. The idea that un-
conscious automatic co-operation exists has had a
long history, and yet it is just now beginning to
escape from the heterodox category.
My own interest in this subject dates not from a
preconceived idea but from a clearly remembered
bump against some stubborn experiments. Almost
thirty years ago as a graduate student in zoology I
was engaged in studying the behavior of some com-
mon small fresh-water animals called isopods, tiny
relatives of the crayfish. All fall and winter I had
been collecting them from quiet mud-bottomed
ponds, chopping the ice if necessary, and from be-
neath stones and under leaves in clear small streams.
I kept them in the laboratory under conditions
which resembled those in which they lived in na-
ture. Then day after day I put lots of five or ten
isopods into shallow water in a round pan that had
a sanded wax bottom so prepared that the isopods
20
HISTORY AND NATURAL HISTORY 21
could crawl about readily. When a current was
stirred in the water the isopods from the streams
usually headed against it; but those from ponds were
more likely to head down current, or to be indif-
ferent in their reaction to the current. The behavior
of the two types was sufficiently different so that at
first I thought that stream and pond isopods repre-
sented different species, but the specialist at the
National Museum assured me that all belonged to
the species appropriately called Asellus communis,
the commonest isopod of our inland waters.
Rather cockily I reported after a time to my in-
structor that I had gained control of the reaction of
these animals to a water current. By the judicious
use of oxygen in the water, I could send the indif-
ferent pond isopods hauling themselves upstream, or
I could reduce the stream isopods to going with the
current. I had not reckoned with another factor that
presently caught up with me.
After a winter in the laboratory it seemed wise as
well as pleasant to take my pan out to a comfortable
streamside one sunny April day, and there check the
behavior of freshly collected isopods in water dipped
from the brook in which they had been living. To
my surprise, the stream isopods, whose fellows all
winter had gone against the current, now went
steadily downstream or cut across it at any angle to
22 THE SOCIAL LIFE OF ANIMALS
reach another near-by isopod. When I used five or
ten individuals at a time, as I had done in the labo-
ratory, they piled together in small close clusters
that rolled over and over in the gentle current.
Only by testing them singly could I get away from
this group behavior and obtain a response to the
current; and even this reaction was disconcertingly
erratic.
It took another year of hard work to get this con-
tradictory behavior even approximately untangled;
(i) * to find under what conditions the attraction of
the group is automatically more impelling than keep-
ing footing in the stream; and that was only the
beginning of the road that I have kept from that
April day to this time, continuing to be increasingly
absorbed in the problems of group behavior and
other mass reactions, not only of isopods, but of all
kinds of animals.
As the years have gone on, aided by student and
other collaborators and by the work of independent
investigators, I have tried to explore experimentally
the implications of group actions of animals. And
necessarily, too, I have had to turn to the world's
literature to find what others have done and are
doing along this line.
* Detailed citations to more complete statements will be found in
the bibliography.
HISTORY AND NATURAL HISTORY 23
A Greek philosopher named Empedocles seems
to have had the first recorded glimmerings of an
idea of the universal and fundamental nature of
co-operation which underlies group action, as well
as a conception of the opposing principle of the
struggle for existence. Empedocles lived in the fifth
century B.C., and he was not only a thinker but so
much a man of affairs that he was offered a king's
crown, which he refused. (128)
He owes his present-day fame to two long poems
in which he outlined the idea that there are natural
elements: fire, earth, air, and water, which are acted
upon by the combining power of love and the dis-
rupting power of hate. Under the guidance of the
building force of love the separate elements came
together and formed the world. Separate parts of
plants and various unassorted pieces of animals arose
from the earth. These, Empedocles taught, were
often combined and at first the results were mon-
strous shapes, which in time became straightened
around until, still guided by combining love, they
clicked, to make the more perfect animals we now
know. It has taken us almost two and a half mil-
lennia to transmute this poetic conception into the
less picturesque but more exact and workable ex-
pression acceptable to modern science.
After the fertile Greek era there intervened in this
24 THE SOCIAL LIFE OF ANIMALS
field as elsewhere the long sterile period when Greek
philosophy, if known, was dogmatically accepted,
and shared with other authoritarian systems the re-
sponsibility of explaining the world of reality as well
as the universe of fancy.
It was not until my own experiments and think-
ing and reading had begun to form in my mind a
fairly definite pattern that, by the aid of Havelock
Ellis's The Dance of Life (43) I stumbled upon the
ideas of the third Earl of Shaftesbury, who lived be-
fore and after 1700. He seems to have been the first
intellectual in the modern period to recognize fairly
clearly that nature presents a racial impulse that has
regard for others, as well as a drive for individual
self-preservation; that, in fact, there are racial drives
that go beyond personal advantage, and can only be
explained by their advantage to the group.
An unfriendly contemporary wrote pretty much
these words: "Shaftesbury seems to require and ex-
pect goodness in his species as we do a sweet taste in
grapes and China oranges, of which, if any are sour,
we boldly proclaim that they are not come to their
accustomed perfection." Havelock Ellis, in reviewing
this development, says that "therewith 'goodness*
was seen practically for the first time in the modern
period to be as 'natural' as the sweetness of ripe
fruit." It is only fair to record that in the religious
HISTORY AND NATURAL HISTORY 25
world for at least fifty years previous there had been
growing a similar conviction among certain heretics.
In 1930, after having written the text of a care-
ful account of experimental evidence concerning the
existence and non-existence of co-operation at sub-
social levels, (3) I set down in the draft of a proposed
preface that the existence of such a principle was
now for the first time an established fact, for which
the details to follow gave full proof. I still think
that the proof is good. However, the preface as
published does not contain any such claim, for at
that point in the writing I went back and re-read
Des societes animales by the French scientist Es-
pinas, (44) which appeared in 1878 and which was
the pioneering essay in this field so far as modern
work is concerned. There I found Espinas affirming
that no living being is solitary, but that from the
lowest to the highest each is normally immersed in
some sort of social life, a fact which he proclaimed
sixty years ago, and added that he was ready to offer
conclusive proof.
I turned through the pages past his detailed his-
tory of the evolution of ideas about the origin and
development of society, and read his massed evi-
dence that communal life is not "a restricted acci-
dental condition found only among such privileged
26 THE SOCIAL LIFE OF ANIMALS
species as bees, ants, beavers and men, but is in fact
universal."
The evidence was largely based on observations
of the existence of animal groupings in nature,
which are found widely distributed in the different
levels of the animal kingdom— facts such as I shall
review later in this chapter. It was clear to me that
the facts which Espinas had found so impressive had
not convinced others and, while suggestive, did not
seem compelling to me in the light of other indica-
tions to the contrary. Perhaps, I cautioned myself,
even the experimental evidence that I had accumu-
lated in 1930 was not really crucial, and it would
be well to avoid making too strong a claim in the
matter. The same caution must continue even in the
face of still stronger evidence known today.
The conclusions of Espinas coming in 1878 are
the more important because the scientific world was
then, as men in the street are today, under the spell
of the idea that there is an intense and frequently
very personal struggle for existence so important and
far reaching as to leave no room for so-called softer
philosophies. The idea of the existence of natural
co-operation was apparently in the air despite the
preoccupation with this phase of Darwinism. Kessler
is said to have addressed a Russian congress of natu-
ralists on this subject in 1880, and from this ad-
HISTORY AND NATURAL HISTORY 2?
dress sprang the remarkable if uncritical book by
the Russian anarchist, Prince Kropotkin, on mutual
aid. (74)
By combing the accumulated natural history rec-
ords, Kropotkin was able to collect observation after
observation which indicated that animals in nature
do aid each other to live, as well as, on occasion, kill
each other off. Kropotkin's work served the admi-
rable purpose of keeping this idea alive and popu-
larizing it. It has had also the less fortunate result
of bringing Kropotkin's fundamental doctrine into
disrepute among students who are critically sensi-
tive to the value of evidence, and who find that
Kropotkin's sources were not always reliable.
William Patten, an American biologist who taught
for many years at Dartmouth College, made the next
general statement of the fundamental nature of co-
operation when in 1920 he gave it a central place
in his analysis of the grand strategy of evolution, (go)
It is of personal interest to me that at the scientific
meetings in 1919 at which I presented my first ex-
perimental results on this subject, Professor Patten
gave a vice-presidential address in which he outlined,
mainly from philosophical considerations, his con-
clusions concerning the importance of biological
co-operation. He was rightly impressed by the fact
that cells originally were separate, as protozoans are
28 THE SOCIAL LIFE OF ANIMALS
today. Some, however, evolved the habit of remain-
ing attached together after division. This made a
beginning from which the many-celled higher ani-
mals could develop. With each increase in the ability
of cells to co-operate together there came power to
increase the complexity of organization of the cell
masses. The highly evolved bodies of men and of
insects are thus an expression of increasing inter-
cellular co-operation which finally reaches a point
at which, for many purposes, the individual person
becomes the unit rather than the co-operating cells
of which he is composed.
About the same time the German, Deegener, (40)
published an extensive treatise on the social life of
animals, along the same lines as the book written
by Espinas forty years before. Deegener 's distinctive
contribution was a classification of the different
social levels, from the simplest sorts of artificial col-
lections of animals to parasitism and truly social
life. His rating of these different aspects of sub-social
and social life in one long outline has the great
merit of showing that there are no hard and fast
lines which can be drawn between social and sub-
social organisms, but that social communities are
the natural outgrowth of sub-social groupings. Un-
fortunately, wdth Teutonic vigor and vocabulary,
he designated the different categories in words as
HISTORY AND NATURAL HISTORY 29
unwieldy as they were exact. Bogged down by the
weight of such terms as sympatrogynopaedium, syn-
aporium and heterosymphagopaedium, Deegener's
real contribution tends to be lost even to biological
scholars.
A survey such as I am attempting here should not
try to be exhaustive; I shall dismiss with a word the
slight advance made by Alverdes (16) and the work
of many others without that. There is, however,
another phase of the literature whose reading has
given me so much pleasure as well as useful infor-
mation that I shall not pass it over: this deals with
the social insects. Espinas, Kropotkin, Deegener and
Alverdes of those mentioned, and a host of others,
have written in detail and in general about these
fascinating insects, but none more accurately or
with greater insight and literary as well as scientific
skill than the American entomologist, William
Morton Wheeler. His book on Social Life Among
the Insects, which appeared in 1923, is a noteworthy
general summary. (120) In this he shows that among
insects alone, and including such well-known forms
as termites, bees, wasps and ants, and the less gen-
erally known social beetles, the social habit has
arisen some twenty-four distinct times in about one-
fifth of the known major divisions of insects. It
would seem that there is a general reservoir of pre-
30 THE SOCIAL LIFE OF ANIMALS
social traits from which, given the proper opportu-
nity, society readily emerges. Wheeler, no less than
Espinas, from whom he quotes, emphasizes that even
so-called solitary species of animals are of necessity
more or less co-operative members of associations of
animals and that animals not only compete among
themselves but they also co-operate with each other
to secure mates and insure greater safety.
It did not, however, make for the full acceptance
of these ideas that Wheeler drew his illustrative
material primarily from, and based his conclusions
mainly on, his knowledge of social life among in-
sects. The existence of co-operation among nest
mates in ants and bees does not prove that there are
beginnings of co-operative processes among amoebae
and other greatly generalized animals.
Man and the few species of highly social insects
are a small part of the animal kingdom; in order
to discover and distinguish the principles of general
sociology it is necessary to look farther, to focus
attention on the social and anti-social relationships
of many animals usually regarded as lacking social
life.
With and without this end in view there have
been in the last twenty years simultaneous but inde-
pendent outbreaks of experimentation on group
effects among the lower animals. For a time just
HISTORY AND NATURAL HISTORY 31
preceding and following 1920 we, who in Aus-
tralia, (107) in France (26) and in the United
States (2) were engaged in these studies, continued
unaware of each other's work. Relatively soon, how-
ever, since biological world literature is today widely
and promptly circulated, all such work, even that
in Russia, (53) became generally known. It is these
general experiments on population growth, on mass
physiology and on animal aggregations, that are now
the important aspect of the field of animal co-
operation.
I have briefly traced here the history of the idea
of innate co-operation. One reason for the slowness
of accepting that idea is the obvious fact that co-
operation is not always plain to the eye, and that
competition in its most non-co-operative form, in
which no social values are apparent, can readily be
observed. With certain exceptions to be nientioned
soon, it has seemed that, social species aside, crowd-
ing, the simplest start toward social life which is
easily apparent and a condition of nearly all society,
was harmful alike to the individual and to the race.
It has been known from experimental evidence
since 1854 (62) that crowded animals may not grow
at all, or, at any rate, gi-ow less rapidly than their
uncrowded brothers and sisters. And under many
conditions crowded animals not only do not grow.
32 THE SOCIAL LIFE OF ANIMALS
they die more readily, and frequently they repro-
duce less rapidly than if living in uncrowded popu-
lations.
All the older works in natural history taught
fairly clearly that crowded groups, to have real sur-
vival values, must be sufficiently well organized to
contribute to group safety by warning of danger or
by defense in case of attack. (3) If, in addition, these
groups are organized on a basis of division of labor,
such as occurs in the highly social colonies of ants
or termites, with specialized reproductives, workers
and soldiers, or according to the patterns found in
human society, then the survival values of groups
are readily seen.
Yet for some reason, under natural conditions and
with very many sorts of animals, crowding in all
degrees does occur and apparently always has oc-
curred. Conceded that animals do not always act for
their own best interests, still they must do so to a
certain degree or be exterminated in the long run.
The advantages of the long-established habit of a
species may not be obviously apparent, but it is not
safe to say offhand that advantages do not exist.
There are the dense crowds of certain animals,
ladybird beetles (Plate la), for example, that with
the approach of winter collect in restricted and fa-
vorable places where they hibernate together. Ap-
PLATE I. a. Ladybird beetles cellect in dense ag-
gregations in the autumn and hibernate. /;. During
their breeding season, male midges gather in swarms
and await the coming of .the females. (Photographs by
Welty.)
HISTORY AND NATURAL HISTORY 33
parently, in the face of winter cold, there is some
safety in numbers even among cold-blooded animals
that collect in hordes without any organization.
A second plain exception to the general testimony
that crowding of non-social species is harmful are
the aggregations that form during the breeding sea-
son. Like the hibernating groups, these are very
widely distributed through the animal kingdom.
Breeding aggregations of worms, crustaceans, fishes,
frogs, snakes, birds and mammals or the midge in-
sects shown in Plate lb, for example, have long at-
tracted attention. Their numbers have been great
enough and conspicuous enough to stimulate re-
peated descriptions by naturalists.
A third exception is found during times of migra-
tion, when animals frequently crowd together in
great hordes and execute mass migratory movements,
like those of many birds.
However, breeding, hibernation and migration
aside, the older information indicated that up until
the point that social life is developed, crowding is
harmful.
But there are many other instances of crowding
which do not fall under any of these classifications;
and it will be worth while to consider here the ex-
tent and the natural history of some of these dense
animal aggregations. Here, as elsewhere, there will
34 THE SOCIAL LIFE OF ANIMALS
be no attempt to catalogue all known instances or
to select merely the very best cases known. I shall
try to use examples that are not too shopworn by
repeated description.
Almost every observant person has seen the soft
green "bloom" which covers many stagnant ponds.
Under the microscope this "bloom" is often seen to
be composed of myriads of the tiny plant-animal
Euglena. These organisms are commonly one-tenth
of a millimeter long, which means that in a char-
acteristic layer of "bloom" there would be at least
sixty to one hundred thousand animals per square
inch; and acres of water are sometimes covered.
Lobster-krills are small crustaceans that occur com-
monly in shoals about the Falkland Islands, Pata-
gonia, New Zealand and other southern waters. (81)
A larval stage of this animal, less than an inch long,
occurs often on the surface of the water in such
numbers that the sea is red for acres; and whales in
those waters simply open their mouths and swim
through slowly, feeding with no more effort than
the process of straining them out. These shrimp-
like animals may be piled up on the shore by tide
and wind in stench-producing layers. Dampier wrote
of them in 1700: "We saw great sholes of small lob-
sters, which colored the sea red in spots for a mile
in compass"; and they have been known to extend
HISTORY AND NATURAL HISTORY 35
along the Patagonian coast for as much as three hun-
dred miles.
At Woods Hole, on Cape Cod, I have at certain
seasons dipped up a bucket of sea water from the
harbor and found more space occupied by clear,
jelly-like ctenophores, each the size of a walnut,
than was taken by water. Sometimes I have dipped
up a fingerbowl of sea water and found it so filled
with small pin-point-like copepods that again there
seemed to be more of them than of the water itself.
These tiny relatives of the lobster-krills are also the
food of whales, and they, too, may discolor the
ocean for miles.
Around bodies of fresh water, may-flies or midges
may emerge in clouds. At Put-in-Bay, near the
lights flooding the monument that commemorates
Perry's victory, I have picked up living may-flies by
the double handfuls from the millions that fly to-
ward the lights; and near by our lake boat steamed
through windrows of cast skins of the emerging may-
fly nymphs. Nearer Chicago I have taken water
isopods, the half-inch crustaceans mentioned earlier,
by the bucketfuls from pools where they had col-
lected in numbers only to be compared with those
in twenty swarms of bees.
We have already spoken of the migratory hordes.
Locusts in migration (116) swarm out of the sky in
36 THE SOCIAL LIFE OF ANIMALS
the Sahara borderlands, in southern Russia, in
South Africa and on the Malay Peninsula in ter-
rorizing numbers (Figure 1). They once did so on the
Great Plains of the United States, leaving a lively
memory of destruction that is still roused by the
smaller migrations that may occur there any summer
^''' ^ ■.■:,:■:. . ■■ . -•■•■■■•• \
Fig. 1. A band of grasshopper nymphs on the march.
(From Uvarov, by permission of the Imperial Bureau of
Entomology.)
in spite of active control measures. I myself have
seen the so-called Mormon cricket advancing from
the relatively barren mountain pastures of Utah
into the green fields in numbers which were not
halted by the hawks, turkeys and snakes attendant
on the swarm and feeding greedily; or the active
assaults of men and children warned out to protect
the cultivated lands. Migrating army worms and
chinch bugs present equally impressive aggregations.
The emergence of Mexican free-tailed bats from
the Carlsbad cave of an August evening has been
described as a black cloud pouring out in such den-
sity as to be visible two miles away. (19) Such bats
HISTORY AND NATURAL HISTORY 37
are estimated to hibernate in these caves by the
milHons; and they may be found through the day
in sleeping masses a yard across, hanging from the
roof like a swarm of bees.
Even larger mammals may collect into great,
closely packed herds. The migrating caribou on
the tundra are said to pour south in hordes that
flow past a given point for hours or even for days.
And of the antelope on the plains of Mongolia, (17)
Roy Chapman Andrews says that he has seen thou-
sands upon thousands of bucks, does, and fawns
pour over the rim and spread out on the plain.
Sometimes a thousand, more or less, would dash
away from the fierd, only to stop abruptly and feed.
The mass of antelope were in constant motion even
when the animals were undisturbed. They scattered
before his automobile only to re-form within a few
hours. In that region only the grassland antelope
gathers in such immense herds; the long-tailed
desert species never does so, probably because there
is not enough food to support them in their more
arid dwelling place.
These are merely a few of the more dramatic
instances of the collection of great masses of animals
in a small space. They are more spectacular but
probably less important than are the innumerable
smaller aggregations of animals which are frequently
38 THE SOCIAL LIFE OF ANIMALS
encountered. The small dense crowds of whirligig
beetles are a case in point. These occur in wide-
spread abundance on the surface of our inland
waters.
The more common condition of less intense crowd-
ing does not mean that animals are usually solitary.
Rather, the growing weight of evidence indicates
that animals are rarely solitary; that they are almost
necessarily members of loosely integrated racial and
interracial communities, in part woven together by
environmental factors, and in part by mutual attrac-
tion between the individual members of the different
communities, no one of which can be affected with-
out changing all the rest, at least to some slight
extent.
Let us take an example. Before the coming of the
white man, and even a century ago or less, much of
the Great Plains was occupied by what ecologists
call a grassland-bison community. (4) Grasses could
readily grow in the rich soil, even with the usual
summer dry spells and the more severe cyclic
drouths that occurred even then. By keeping the
grasses fairly closely cropped the bison herds pre-
vented the invasion of herbs and shrubs that might
have withstood the severities of the climate but
could not make headway against continual grazing
(Plate II). In this function the bison were joined by
PLATE II. A giasslancl-bison community. (Photo-
graph from the National Park Board of Canada.)
HISTORY AND NATURAL HISTORY 39
a myriad of grasshoppers, crickets, meadow mice
and prairie dogs. All these were key-industry ani-
mals. In one way or another they converted the grass
into meat of different sorts, on which the plains
Indians, buffalo wolves, haw^ks, owls, and prairie
chickens fed. If the grass failed, then many of the
key-industry herb-eaters and those that in turn fed
on them must either starve, migrate into another
community where they would be disturbing factors,
or change their source of food and thereby disturb
the balance in their own community.
It must be pointed out here that the plants of this
community cannot be set off as separate from the
animals. They divide the available space between
them; they constantly interact upon each other and
upon their physical environment; except for pur-
poses of formal study or in limited fields, the biolo-
gist must consider both as members of a given
association.
In such a community the effects of the dominant
bison were felt in times of stress by the humblest
and least conspicuous grasshopper. In the spring of
the year hundreds of square miles normally sup-
ported populations of six to ten million insects and
other invertebrate animals for every acre of land.
As with warmer weather the predatory animals re-
turned to the grasslands, these insects were eaten off
40 THE SOCIAL LIFE OF ANIMALS
until perhaps a tenth of their number could be
found later in the season; with the autumn lushness
they increased again, only to fall back to some half-
million or so per acre during the winter cold.
Similar communities exist among aquatic forms.
In fact one of the first demonstrations of such a
community was made for the animals living in and
on an oyster-bank. (82) A beautiful and penetrating
description of the interrelations that may be found
in a small lake was published not long after by the
late Professor Forbes (48) of the Illinois Biological
Survey, in which he pointed out that minnows com-
peted with bladderwort plants for key-industry or-
ganisms; and showed that when a black bass is
hooked and taken from the water the triumphant
fisherman is breaking, unsensed by him, myriads of
meshes which have bound the fish to all of the dif-
ferent forms of lake life.
The existence of these communities is now gen-
erally recognized, and in order that they may exist
it seems that there must be a far-reaching, even if
vague and wholly unconscious, co-operation among
all the living creatures of the community. It is to
such relationships that Wheeler referred when he
said, "Even the so-called solitary species are neces-
sarily more or less co-operative members of groups
or associations of animals of different species."
HISTORY AND NATURAL HISTORY 41
Within these communities aggregations of animals
occur for a variety of reasons. Their nature can best
be shown by a series of illustrations.
One variety of aggregations is that of colonial
forms, in which many different so-called individuals
remain through life permanently attached together.
In the simplest cases all the individuals are alike.
Each possesses a mouth and food-catching tentacles,
and each feeds primarily for itself, although food
caught by one individual may be shared with others
near by. In more complex forms some individuals
have the mouths suppressed, and receive all their
food from those that do take food. They have be-
come specialized as bearers of batteries of stinging
cells; they strike actively when the colony is touched,
and their stinging cells explode so effectively as to
give protection to the colony. Other individuals in
the same colony bear medusa-like heads which break
away and swim off, producing eggs and sperm, dis-
tributing them as they drift. Here is certainly a divi-
sion of labor though these colonial animals are
never rated as social.
Various modifications of such colonial animals
are found particularly among the colonial protozoa,
sponges and the coelenterates; they also occur higher
in the animal kingdom, even among the lower
chordates, the great phylum to which man himself
42 THE SOCIAL LIFE OF ANIMALS
belongs. It is interesting that animals whose struc-
ture forces them to the sort of compulsory mutual
aid that automatically follows such structural con-
tinuity have never progressed far either in social
achievement or in the evolutionary scale. When
higher animals, such as the lower chordates, show
this development they are usually regarded as de-
generate members of their general stock. These
colonial animals are seldom dominant elements in
the major communities of which they are a part.
One comes to the conclusion that the more nearly
voluntary such co-operation is, the greater its ad-
vantage in social life. It might on the other hand
be pointed out that when an animal has achieved
social organization and division of labor low in the
evolutionary scale, the resulting colonies are so well
adapted to their environment that there is not suffi-
cient pressure to cause evolutionary changes.
A second type of aggregation occurs when animals
are forced together willy-nilly by the action of wind
or tidal currents or waves over which they have no
control, and whose effects they cannot resist. Many
of the masses which lend color to wide patches of
the ocean surface are brought together by tempo-
rary or permanent currents. Often animals so dis-
tributed are thrown down more or less by chance
on types of bottom on which they can develop, and
HISTORY AND NATURAL HISTORY 43
there, if favorable niches are somewhat rare, dense
aggregations may result, like New England coral on
a suitably hard bottom, or the animals found on a
wharf piling.
These accidental animal groupings may persist
only as long as the physical forces which brought
them together continue to act. Usually, however,
they last somewhat longer, as a result of a slightly
positive social inertia which tends to keep animals
concentrated in whatever place they happen to be
found. If the groupings are to have much perma-
nence this quality of social inertia, the tendency of
animals to continue repeating the same action in
the same place, must be reinforced by another
quality: the social force of toleration for the pres-
ence of others in a limited space. The densely packed
communities of animals on a wharf piling can per-
sist only if toleration for crowding is well developed.
Other dense collections may be brought about by
forced movements of animals in response to some
orienting influence in their environment. These
oriented, compelled reactions are frequently called
tropisms. They are shown by the moths or June
beetles or may-flies that collect about lights. Such
aggregations are a result of the inherited, internal
organization of the animals; and the irresistible at-
traction of the may-fly to the light is joined with
44 THE SOCIAL LIFE OF ANIMALS
active toleration for the close proximity of others.
Similarly close aggregations occur as a result of
the less spectacular trial and error reactions, in
which the animals wander here and there, more or
less vaguely stimulated by internal physiological
states or external conditions, and so come to collect
in favorable locations. Collections of animals about
limited sources of food give a good illustration.
These, too, may show only the social qualities of
inertia and toleration.
A decided advance is made when animals react
positively to each other and so actively collect to-
gether, not primarily because the location is favor-
able or through environmental compulsion, but as
the result of the beginnings of a social appetite. In
early stages of such reactions, the movement together
may come primarily because the collection of isopods
or earthworms or starfishes are substitutes for miss-
ing elements in the environment.
Take, for example, the snake or brittle starfishes
of the New England coast. These are rare now along
Cape Cod, but before the wasting disease swept away
the eel grass they were abundant in favorable locali-
ties, but were rarely found close together. I have
spent hours peering down through a glass-bottomed
bucket here and there and round about in one of
these localities, and have not seen more than one
PLATE III. a. Brittle starfish aggregate readily
when put into a bare vessel of sea watei . b shows con-
ditions ten minutes after a was taken. (Photographs by
Welty.)
HISTORY AND NATURAL HISTORY 45
at a time. And I have spent more hours wielding a
sturdy garden rake in swathe after swathe through
the short eel grass, very rarely pulling in more than
one starfish at a haul.
Yet when a few brittle starfishes are placed in a
clean bucket of sea water they clump together like
magic (Plate III). In bare laboratory aquaria they
remain so clumped for weeks; in fact the aggrega-
tions become more compact as time goes on as the
animals bring back their extending arms and tuck
them into the mass. If, however, the aquaria are
dressed up by the introduction of eel grass so that
conditions approach those found in nature, the ag-
gregations disperse and the starfishes climb actively
about over the blades of the eel grass, feeding on
organisms and debris found on their surfaces.
The idea that in clean laboratory dishes these star-
fishes are substituting each other for the missing eel
grass was obvious and easy to test. A kind of artifi-
cial eel grass was made of glass rods twisted in
various shapes so that they offered a supporting
framework for climbing in much the same way as
the true eel grass. So long as the rods remained the
starfishes clambered about over the meshwork or
hung motionless, usually isolated. If the rods were
removed they again clustered together.
As I have said elsewhere, (3) it is a far cry from
46 THE SOCIAL LIFE OF ANIMALS
such aggregations to the groupings of foreigners in
a strange city that result in Little Italy, or the
Mexican settlement, or a German quarter; and yet
basically some of the factors involved are similar.
Perhaps there is a closer connection between such
aggregations in the wide expanse of a clean aqua-
rium and the schooling tendency found among
many fishes of the open sea; perhaps the same phe-
nomenon accounts for the flocking tendency of
many birds, as well as mammals on the equally
monotonous grassy seas of temperate plains.
A somewhat different expression of a positive
social reaction is shown when animals that are
usually more or less isolated come together and pass
the night grouped as though they were engaged in
a slumber party. This type of behavior has been
repeatedly described for different insects, even for
the wasps that remain separate to such an extent
that they are called solitary wasps. In some forms of
solitary wasps both males and females are found in
the sleeping group. With solitary bees, such as we
have near Chicago, the overnight aggregations are
composed of males only. A study which was made
of the sleeping habits of a Florida butterfly species
indicates that these Heliconii (69) come together
night after night in the same location, in part at
least as a result of place-memory. The assemblages
HISTORY AND NATURAL HISTORY 47
lack sexual significance. There is some protection in
the fact that if one is disturbed the whole group may
be warned. The presence of many butterflies would
reinforce any species odor that might attract others
of the same species, or repel possible predators.
The crowded roosts to which certain birds return
not only for one season but sometimes for years are
widely known. Here again we are concerned with a
positive social appetite which grows stronger with
the approach of darkness; the details as to why and
how it operates are not known.
Animals which come together in intermittent
groupings like these overnight aggregations are
showing a social appetite which is none the less
real because it is effective only at spaced intervals.
In this it resembles other appetites such as those
for food, water and sex relations. From such occa-
sional or cyclic expressions of a social appetite it is
a relatively short step to whole modes of life which
are dominated by a drive for social relationships.
As I have already said, in the insects alone this step
has been taken some twenty-four distinct times and
in widely separated divisions of that immense group.
Normally the development of highly social life
comes by way of an extension of sexual and family
relations over greater portions of the life span.
Here again all degrees of increased length of asso-
48 THE SOCIAL LIFE OF ANIMALS
elation can be shown, from the sexual forms that
meet but once and for a brief moment to the ter-
mite kings and queens that live together for years.
Also all stages exist in the evolution of the associa-
tion of parents with offspring, from the insects like
the female walking-stick, which deposits eggs as she
moves about and pays no more attention to them,
to the ants and bees whose worker offspring spend
their entire lives in the parental colony or some
colony budding off from it.
While the extension of family relations is very
obviously one potent method by which social life is
developed to a high level, there are other social
groupings which also deserve consideration in con-
nection with the problem as to the method of evo-
lution of social life. Schools of fish arise, for exam-
ple, under conditions in which there is no associa-
tion with either parent after the eggs are laid. At
times the eggs may be so scattered in the laying that
the schools form from unrelated individuals. Here
the schooling tendency seems to underlie rather
than grow out of family life. The mixed flocks (22)
of tropical birds which are composed of many spe-
cies obviously did not grow directly from family
gatherings, and the groups of stags of Scottish deer,
probably the original stag parties, (38) appear to
give evidence of a grouping tendency independent
HISTORY AND NATURAL HISTORY 49
of intersexual or family relations. This subject will
be discussed in more detail in the final chapter.
The conclusion seems inescapable that the more
closely-knit societies arose from some sort of simple
aggregation, frequently, but not necessarily, solely
of the sexual-familial pattern. Such an evolution
could come about most readily with the existence
of an underlying pervasive element of unconscious
co-operation, or automatic tendency toward mutual
aid among animals.
In the simpler aggregations evidence for the pres-
ence of such co-operation comes from the demon-
stration of survival values for the group. These are
more impressive the more constant they are found
to be. If they exist throughout the year they are
much more important as social forerunners than if
present only during the mating season or at times
of hibernation.
Ill
■ Beginnings of Co-operation
WITH this chapter I begin the presentation of the
evidence for the assertion that there is a general prin-
ciple of automatic co-operation which is one of the
fundamental biological principles. The simplest ex-
pression of this is often found in the beneficial ef-
fects of numbers of animals present in a population.
Laboratory work of the last two decades still shows
that overcrowding is harmful, but it has also uncov-
ered a no less real, though somewhat slighter, set of
ill effects of undercrowding.
To be sure, overcrowding always produces ill ef-
fects, and these can always be demonstrated at some
population density. On the other hand, the ill effects
of undercrowding cannot always be shown, though
frequently they can. In generalized curves the mat-
ter may be summarized thus: Under certain condi-
tions (g6) we find the curve running like the dia-
gram in Figure 2 A, when height above base line
gives the rate of the biological action being meas-
ured, and distance to the right shows a steadily in-
50
BEGINNINGS OF CO-OPERATION 51
creasing population. Under these conditions only
the ill effects of overcrowding are visible, and the
optimum population is the lowest possible. This is
the modern expression of what used to be called the
struggle for existence. In the more poetic post-Dar-
winian days this struggle was thought of as so in-
tense and so personal that an improved fork in a
bristle or a sharper claw or an oilier feather might
turn the balance toward the favored animal. Now
we find the struggle for existence mainly a matter
of populations, measured in the long run only, and
then by slight shifts in the ratio of births to deaths.
A second type of phenomena is represented by a
curve with a hump near the middle (97) as shown in
Figure 2B.
Again, height above the base line measures the
speed of some essential biological process or proc-
esses, such as longevity; distance to the right gives
increasing population densities. The harmful effects
of overcrowding, indicated by the long slope to the
right, are still plainly evident, but there is also ap-
parent a set of ill effects associated with undercrowd-
ing which are shown by the downward slope to the
left. Many have written pointedly about overcrowd-
ing, and while there is still much to be learned in
that field, it is in the recently demonstrated exist-
ence of undercrowding, its mechanisms and its im-
52
THE SOCIAL LIFE OF ANIMALS
plications, that freshness lies. Without for one min-
ute forgetting or minimizing the importance of the
right-hand limb of the last curve, it is for the more
romantic left-hand slope that I ask your attention.
Fig. 2. A. Under some conditions the rate of bio-
logical action which is being measured is greatest with
the smallest population, and decreases as the numbers
increase. B. Under other conditions there is a distinct
decrease in the rate of the measured biological reaction
with undercrowding (to the left) as well as overcrowding
(to the right).
Perhaps the simplest and most direct demonstra-
tion of certain harmful effects of undercrowding
comes from an experiment which I understand is
carried on spontaneously among undergraduate men
at certain universities and colleges of which X, or
perhaps better, Y, is an example. A certain number
of men gather together in a limited space under arti-
ficial light and undertake to consume a more or less
limited amount of stronger or weaker alcohol. If
BEGINNINGS OF CO-OPERATION 53
there are many men present in proportion to the
amount of alcohol, relatively little or no harm will
result from the experiment. If there are very few
men and much alcohol there may be garage bills and
other important repairs to be made.
In one way or another similar tests have been car-
ried out in the laboratory with a variety of poisons,
and many kinds of animals. Again I choose from
the mass of available evidence the results of a simple
and clean-cut experiment to illustrate the same point
with non-human animals.
Everyone is acquainted with goldfish; they are
hardy forms or else they would not be alive today
in so many goldfish bowls. Colloidal silver in its
commercial form of argyrol is also well known. Col-
loidal silver, that is, the finely divided and dispersed
suspension of metallic silver, is highly toxic to liv-
ing things, including even the hardy goldfish.
In the experiment in our laboratory (8) we ex-
posed sets of ten goldfish in one liter of colloidal
silver, and at the same time placed sets of ten simi-
lar goldfish, one each, in a whole liter of the same
strength of the same suspension. This was repeated
until we had killed seven lots of ten goldfish and
their seventy accompanying but isolated fellows.
Then when the results were thrown together we had
the simple table on page 54.
t^- I
54 THE SOCIAL LIFE OF ANIMALS
TABLE I
Survival in minutes of goldfish in colloidal silver
NUMBER NUMBER DIFFERENCE STATISTICAL
GROUPED ISOLATED PROBABILITY
7X lo 70x1
182 min. 507 min. 325 min. P < o.ooi
Any biological experiment has a large number of
so-called variables, that is, of factors that it is diffi-
cult or impossible to bring under such complete
control that we can be certain that the experiment
will be exactly repeatable next time. Hence it is
customary to make experiments if possible as paired
experiments, in which one set of conditions (those
of the group in this instance) will differ from an-
other lot (those of the isolated goldfish) only by the
one difference, in this case of grouping and isolation.
Such results with these fish can then be analyzed
by statistical methods to find the probability of get-
ting like results merely "by chance." These methods
are now so simple that even I can make the calcula-
tions. They are as accepted a technique as is the
paired experiment.
With the goldfish there is less than one chance in
a thousand of getting as great an average difference
with the same number of trials. Technically we say
that probability, or P, for short, is less than 0.0001.
BEGINNINGS OF CO-OPERATION 55
It means the same. Students of statistics have found
that when P z= 0.05 or less, that is, when there are
fewer than five chances in a hundred of such a thing
happening as a result of random sampling or
"chance," there is likely to be something significant
in such results, the more so the smaller the fraction
which P is said to equal.
We make such tests of our experimental results
continually, to find how we are getting on, and I
shall give probabilities repeatedly. In doing so it
must be remembered that these test the data, not
the theory— and that the data may vary significantly
for unknown reasons, even when we think we are
in full control of the situation; and that because
there is only one chance in one hundred, or ten
thousand, or a million that a thing may happen by
"chance" does not mean that it will never happen
through what we call an accident; merely that the
chances of its happening so, our evidence being what
it is, are on the order of one in one hundred, or ten
thousand, or a million.
I will digress even further into the realm of coinci-
dence. A Negro friend of mine spent a summer in
Europe and while in Paris visited the art galleries
of the Louvre. While there he saw a Negro woman
busy looking at pictures and on coming closer dis-
covered that she was his own aunt. Neither had any
56 THE SOCIAL LIFE OF ANIMALS
idea that the other was in Europe. With no pre-
arrangement, what is the probability that an Ameri-
can Negro from Chicago will meet his aunt in the
Louvre? Yet it did happen this once without in any
way shaking the probability principle.
Perhaps the digression is not so great as might ap-
pear at first glance, for we need a slight common
understanding of the practical working of statistical
probability; all of modern science, the more as well
as the less exact, is built on it.
To get back to our goldfish: those in the groups
of ten lived decidedly longer than their fellows ex-
posed singly to the same amount of the same poison;
and significantly so. But why? Others had made that
experiment w^ith smaller animals, and had decided
that the group gave off a mutually protective secre-
tion which would protect that particular species and
none other. One reason that we were working with
goldfish was because they are large enough so that
we could use approved methods of chemical analysis
in finding where the silver went. The balance sheet
from such tests showed that we could account for
all the silver present. With the suspensions which
had held ten fish the silver was almost all precipi-
tated, while in the beakers that had held but one fish
almost all the silver was still suspended.
When exposed to the toxic colloidal silver the
BEGINNINGS OF CO-OPERATION 57
grouped fish shared between them a dose easily fatal
for any one of them; the slime they secreted changed
much of the silver into a less toxic form. In the ex-
periment as set up the suspension was somewhat too
strong for any to survive; with a weaker suspension
some or all of the grouped animals would have lived;
as it was, the group gained for its members a longer
life. In nature, they could have had that many more
minutes for rain to have diluted the water or some
other disturbance to have cleared up the poison and
given the fish a chance for complete recovery.
With other poisons, other mechanisms become
effective in supplying group protection. Grouped
Daphnia, (50) the active water fleas known to all
amateur fish culturists, survive longer in over-alka-
line solutions than daphnids isolated into the same
volume. The reason here is simple. The grouped
animals give off more carbon dioxide, and this neu-
tralizes the alkali. Long before the isolated individual
can accomplish this, it is dead; in the group those
on the outside may succumb, though if the num-
ber present is large enough even they may be able
to live until the environment is brought under tem-
porary control.
Frequently the protective mechanism is much
more complex. With many aquatic animals, other
things being equal, isolated animals consume more
58 THE SOCIAL LIFE OF ANIMALS
oxygen than if two or more share the same amount
of liquid. By one device or another, grouping fre-
quently decreases the rate of respiration. Several of
these devices are known to us. Professor Child
showed many years ago (31) that when animals are
exposed to a strongly toxic material, those with the
higher rate of respiration, though otherwise similar,
die first. This has been applied to group biology by
direct tests, and it has been shown that the group,
by decreasing the rate of oxygen consumption of its
members, makes them more resistant to the action
of relatively strong concentrations of toxic materials.
Perhaps I have said enough to show that under
a variety of conditions groups of animals may be
able to live when isolated individuals would be
killed or at least more severely injured by unaccus-
tomed toxic, chemical elements, strange to their nor-
mal environment.
Will the same relationship hold in the presence
of changes in physical conditions? There is a con-
siderable and growing lot of evidence that massed
animals, even those that can be called cold-blooded,
are harder to kill by temperature changes than are
similar forms when isolated. (51, 126) This interests
us because massing of such animals at the onset of
hibernation was recognized as one of the early ex-
BEGINNINGS OF CO-OPERATION 59
ceptions to the rule, now outgrown, that crowding
is always harmful.
The exploration of temperature relations is a
time-honored field. I prefer to take up a newer
though related area, that of the effects of ultra-violet
radiation, in which I shall present some evidence
so recently collected that it has never been reported
extensively before. A year ago Miss Janet Wilder
and I began exposing the common planarian worm
of this region to ultra-violet radiation, to find
whether there was any group protection from the
well-described lethal effect of ultra-violet light on
these worms. (12)
In lots of twenty, worms of similar size and the
same history were placed together in a petri dish and
exposed to the action of the ultra-violet light long
enough so that they would disintegrate within the
next twelve hours. Half of them, that is, ten worms,
were then placed together in five cubic centimeters
of water and each of the other ten was put into five
cubic centimeters of similar water. Grouped and iso-
lated worms were treated alike in every way, except
that after irradiation together, half were grouped and
half were isolated.
For one purpose or another we have repeated this
simple experiment a great many times with a variety
of waters, and with experimental conditions ade-
6o THE SOCIAL LIFE OF ANIMALS
quately controlled. Some of the things we have found
out are:
If the worms are crowded under the ultra-violet
lamp so that they shade each other, the shaded ones
RAOIATEO RADIATED RAOIATEO RADIATED
enOUPEO 6R0UPEO GROUPED GROUPED
reSTCO TESTED TESTED TESTED
6R0UPEO SINGLY GROUPED SINGLY
148*
247'
RADIATED RADIATED
GROUPED GROUPED
TESTED TESTED
GROUPED SINGLY
267'
IH 168'
tI ItI
ooooojjj HH^oooooJUJ I
137*
140 ^M
P I
aooo4jU
WELL WATER
DISTILLED WATER
Fig. 3. Planarian worms which have been exposed to
ultra-violet radiation disintegrate more rapidly if isolated
than if grouped.
are definitely protected. When such crowding is
eliminated and by constant watching and stirring,
if needed, during exposure, the worms are kept ap-
proximately equally spaced, even then the grouped
worms survive longer than if isolated. Some of the
relationships are shown in Figure 3.
Each block represents the survival time of several
series of worms. The figures at the top of the block
give the average length of survival in minutes. The
blocks are constructed so that the worms surviving
BEGINNINGS OF CO-OPERATION 6l
longer, which in each case are the grouped worms,
are given as lOO per cent, regardless of the time
taken; while the isolated worms, which had been
irradiated in the same dishes as their accompanying
groups, survived on an average of 78 per cent and
77 per cent respectively in the two tests with well
water, and only 61 per cent in the test in dis-
tilled water. The numbers between the blocks show
the number of worms averaged for each block; that
is, the number of pairs of worms for which results
are summarized. The statistical significance given
in terms of 'T" is very high in each case.
The number present during exposure is impor-
tant, as well as the number present during the time
when it is being determined how long the animals
will survive. Such data are summarized in Figure 4,
which is built exactly on the same principle as that
preceding. Worms radiated when crowded (left-hand
block), and then tested when isolated, survived 517
minutes, while accompanying worms which had been
radiated singly as well as tested when isolated, lived
only 24 per cent as long. Those radiated in a group
and tested singly (middle block) lived 55 per cent as
long as those which had been radiated in a crowd
and then were isolated to observe the effects of radi-
ation. It will be remembered that these crowded
worms actually shaded each other and so gave
62 THE SOCIAL LIFE OF ANIMALS
physical protection from the ill effects of ultra-violet
light. Finally (on the extreme right) is diagramed
the fact that worms radiated and tested singly lived
only 62 per cent as long as those radiated in a group
RAOIATCO RAOIArCO RADIATES RADIATEO RADIATED RADIATED
CROWDED SINGLY CROWDED CROUPtO GROUPED SINGLY
TESTED TESTED TESTED TESTED TESTED TESTED
Singly singly Singly singly singly singly
517' 517' 107'
WELL WATER
Fig. 4. Planarian worms survive exposure to ultra-
violet radiation better if much crowded while being
radiated, or even partially crowded, even though all are
isolated after a few minutes of irradiation.
of 20 per 20 cubic centimeters and also tested singly.
Again the figures give the number of pairs tested
and under "P" the statistical probability, which
shows that all these must be taken seriously even
though there is decreasing significance as the per-
centage of difference of average survival time de-
creases.
In the two cases just outlined mass protection has
been demonstrated, first against the presence of toxic
BEGINNINGS OF CO-OPERATION 63
materials, and second against the ill effects of expo-
sure to lethal ultra-violet rays. To complete the pic-
ture I have now to describe the results of exposing
animals to harmful conditions in which the difficulty
is caused by the absence of elements normally pres-
ent in their natural environment. The experiment
has been made on aquatic animals in a number of
ways, for example, by putting fresh-water animals
into distilled water; but it is easier to demonstrate
when marine animals are placed in fresh water.
Again I select one experimental case from several
available. Near Woods Hole, on Cape Cod, a small
flatworm Procerodes (Figure 5) lives in certain re-
stricted areas in large numbers. They are most abun-
dant along a stony stretch at about the low tidemark
or a little beyond it. (5) There, if one finds the proper
location, one may take from ten to fifty flatworms
from the lower surface of a single stone. Usually
they are more or less clumped together. They are
not easy to see since each is only a few millimeters
long and all are of a dull gray color. Once seen,
they are hard to detach, for the posterior end has a
muscular sucker, by means of which the animal can
cling pretty securely even to smooth stones. When
these worms are put into fresh water, pond water for
example, they swell greatly and soon begin to dis-
integrate.
64
THE SOCIAL LIFE OF ANIMALS
If these flatworms are washed thoroughly to re-
move sea water from their surfaces, and then placed
in fresh water, a certain proportion of the grouped
Fig. 5. The small marine flatworm Procerodes.
animals survive decidedly longer than isolated worms.
The first worms to die in the group do so almost
as soon as the first isolated worms. As the dead worm
disintegrates it changes the surrounding water; we
say it conditions it; and as a result of this condition-
ing the remaining worms of the group have a bet-
ter chance of life.
BEGINNINGS OF CO-OPERATION 65
For more careful experimentation, a sort of worm
soup was prepared by killing a number of well-
washed worms and allowing them to remain in the
water in which they had died and so condition it.
Freshly collected Procerodes lived longer in such
conditioned water than their fellows which were
isolated into uncontaminated, clean pond water. The
difference between the two waters was only that
caused by the fact that in one the worms had died
and disintegrated, while the other was clean. This
difference in survival persisted even when, to make
the test more revealing, the total amount of salt in
the two waters was made identical by adding some
dilute sea water to the clean pond water. Results
from these experiments are shown in Figure 6. In
this chart, distance above the base line gives the
percentage of survival, and distance to the right
shows time of exposure. It will be noted that the
worms lived decidedly longer in the conditioned
water than they did in dilute sea water of the same
strength of salts.
The mechanism of this superficially mysterious
group protection is now known. (86) The dead and
disintegrating worms, or more slowly, the living
worms, give off calcium into the surrounding water,
and calcium has a protective action for marine ani-
mals placed in fresh water or for fresh-water animals
66
THE SOCIAL LIFE OF ANIMALS
put into distilled water, a protective action which is
out of all proportion to its effect in increasing the
osmotic pressure of the water. We can demonstrate
that this is in fact the mechanism of such group
1 Conditioned water
Fig. 6. Procerodes die more rapidly if transferred to
pure fresh water than in dilute sea water, but live
longer if placed in fresh water in which other Procerodes
worms have died, even though the total amount of salt
is the same as in the dilute sea water.
protection. For example, we can analyze the water
which worms have conditioned, find the amount of
calcium that has been added, and by adding that
amount directly get the same results that we do from
the conditioned water.
This explanation is not yet complete— no scientific
explanation ever is— but we have demonstrated that
what was for a time a very mysterious group pro-
BEGINNINGS OF CO-OPERATION 67
tection is in fact in this case an expression of calcium
physiology. The further developments on the sub-
ject await exact information concerning the details
of the physiological effects of calcium.
It is probably of more direct human interest to
■;V*i.;::i:
%^
35
50
60
Fig. 7. Bacteria frequently do not grow if inoculated
in small numbers; here different numbers of Bacillus
coli were inoculated into a medium containing gentian
violet.
know that under many conditions bacteria will not
grow if only a few are inoculated into an animal,
man for example; while with a larger inoculation
they may grow abundantly. (33) Gentian violet is a
poison for many bacteria and in regular medical use
for that purpose. In one well-studied case (Figure 7)
bacteria belonging to the species Bacillus coli failed
to grow on agar containing gentian violet, if singly
inoculated on it; only when thirty or more bacteria
68 THE SOCIAL LIFE OF ANIMALS
were inoculated did steady and regular growth oc-
cur. With the goldfish spoken of earlier, the mass
protection was largely or wholly inoperative when
the group of ten was exposed to ten times the amount
of toxic colloidal silver to which a single fish was
exposed. With these bacteria, however, such quanti-
tative limitations did not hold; thirty organisms
were found to fix at least two hundred times the
amount of poison normally neutralized by an iso-
lated bacterium. This difference between the change
which thirty bacteria can effect together as compared
with what they can accomplish if isolated has been
called an expression of the communal activity of
bacteria. There is a fairly large and growing litera-
ture on this subject which indicates that when only
one or a few bacteria, even if strongly pathogenic,
gain access to the human body, they are likely to
be killed by various devices which aid in resisting
infection. It is fortunate for their victims that bac-
terial infections normally tend not to take unless
the inoculum is somewhat sizable or unless a smaller
dose is frequently repeated.
Mass protection is known to occur among sper-
matozoa. Many animals, especially those that live in
the ocean, shed their eggs and spermatozoa into the
sea water, and fertilization takes place in that me-
dium. Dilute suspensions of such spermatozoa lose
BEGINNINGS OF CO-OPERATION 69
their ability to fertilize eggs much sooner than if
they are present in greater concentration. It is rou-
tine laboratory practice in experimenting with such
animals as the common sea-urchin, Arbacia, to keep
sperm in a cool place, densely massed outside the
body, for hours. Small drops can be withdrawn as
needed for experimentation, greatly diluted and
used almost immediately to fertilize eggs. When such
dilute suspensions have long since lost their fer-
tilizing power the sperm in the original dense mass
are still potentially as active as ever.
So far we have been considering mass effects, the
survival value of which, if any, was shown by in-
creased length of life, often under adverse circum-
stances. Under many different conditions and for a
variety of organisms, the presence of numbers of
forms relatively near each other confers protection
on a part of those grouped together or even on all
present.
It is possible to go a step farther and demonstrate
a more actively positive effect of numbers of or-
ganisms upon each other when they are collected to-
gether. Again I select a fresh case for close scrutiny;
that of crowding upon the rate of development in
sea-urchin eggs.
Arbacia, mentioned above, is the common sea-
urchin of coastal waters south of Cape Cod (Fig-
70 THE SOCIAL LIFE OF ANIMALS
ure 8). It has been much used in studies of various
aspects of development, particularly by the biologists
who gather each summer in the research laboratories
at Woods Hole, Massachusetts. There are several
reasons for its popularity. These urchins are abun-
FiG. 8. Arbacia, the common sea-urchin of southern
New England, shown from the upper surface.
dant in near-by waters and are readily mopped up by
the tubful. They can be kept in good condition for
some days in the float cages, and eggs and sperm
are readily procured as needed. Also the breeding
season of Arbacia extends through July and August,
which are favored months for research at the seaside.
For years biologists at Woods Hole have studied
the embryology and physiology of developing sea-
urchin eggs. They have built up a painstaking,
almost a ritualistic, technique for handling glassware,
BEGINNINGS OF CO-OPERATION 7 I
towels and instruments. The procedures require as
rigid cleanliness as a surgical operation. Conse-
quently it was not surprising when I first took up
their study a few years ago, to have one of my frank-
est friends among the long-time workers on the de-
velopment of Arbacia, voice what was apparently a
common feeling among them. He asked pointedly
if I thought I could come into that well-worked field
and without long training find something they had
overlooked. Such frank skepticism was refreshingly
stimulating and added to the normal zest of bio-
logical prospecting.
The shed eggs of Arhacia are about the size of
pin points and are just visible to the naked eye. The
spermatozoa are tiny things; the individual sperm
are invisible without a microscope although readily
seen when massed in large numbers. When a few
drops of dilute sperm suspension are added to well-
washed eggs, one spermatozoan unites with one q^^.
After some fifty minutes at usual temperatures, the
egg divides into two cells. We call this the first
cleavage. Thirty or forty minutes later a second
cleavage takes place and thereafter cleavages occur
rapidly. Within a day, if all goes well, such an egg
will have developed into a freely swimming larva.
Other things being equal, (lo) the time after fer-
tilization to first, second and third cleavage is speeded
72
THE SOCIAL LIFE OF ANIMALS
up for the crowded eggs. Typical results and some
of the methods are shown in Figure 9. With appro-
4- mm.'
FifSt
Second
% cleai/ed
f^frst
Second
% cieaued.
58.25 60.25
85.83 90.25
99 /GO
Fig. 9. Eggs of the sea-urchin, Arhacia, cleave more
rapidly in dense populations than if only a few are
present. Figures below the diagrams, unless otherwise
indicated, give time in minutes.
priate experimental precautions, some eighteen hun-
dred eggs were introduced into a tiny drop of sea
water. Near by on the same slide forty similar eggs
were placed in a similar drop and the two were
connected by a narrow strait as shown in the figure.
BEGINNINGS OF CO-OPERATION 73
A few eggs from the larger mass spilled over into
this strait. The whole slide was placed in a moist
chamber to avoid drying, and examined from time
to time. In a trifle over fifty-five minutes half the
eggs in the densest drop had passed first cleavage. A
half-minute later, 50 per cent of those in the strait
were cleaved, and twenty seconds later half of the
more isolated ones had divided. The time to 50 per
cent second cleavage ranged between eighty-four
minutes for the crowded eggs and over eighty-six
and a half minutes for the isolated ones.
This was repeated with four thousand eggs or
thereabouts in the denser population, almost six
hundred of which spilled through and formed a flat
apron over the bottom of the second drop, in which
there were thirteen other eggs scattered singly about
the relatively unoccupied space. Under these condi-
tions the time to 50 per cent first cleavage was ap-
proximately fifty-two, fifty-eight and sixty minutes
respectively, and the difference at the middle of the
second cleavage was even greater.
In association with Dr. Gertrude Evans, who is a
good, skeptical research worker, this experiment was
repeated in many different ways; and there remains
in my mind no doubt but that under a variety of
conditions the denser clusters of these Arhacia eggs
74 THE SOCIAL LIFE OF ANIMALS
cleave more rapidly than associated but isolated
fellows.
Under the conditions tested, the stimulating effect
of crowding could be detected when sixty-five or
more eggs were present in the more crowded drop
and twenty-four or fewer eggs made up the accom-
panying sparse population.
Within twenty-four hours, under favorable condi-
tions, one finds one's cultures full of free-swimming
larvae with characteristic arms which are known as
plutei. When all our available data collected the
first day after fertilization are compared there is
again no doubt but that the more crowded cultures
usually develop more rapidly than accompanying but
sparser populations. However, it must be recorded
that throughout the whole series there were occa-
sional isolated eggs that developed as rapidly as the
best of the accompanying denser populations. Such
eggs and embryos were exceptional in our experi-
ence; the fact that they exist indicates clearly that
under the conditions of our experiments crowding,
while usually stimulating, was not absolutely neces-
sary for rapid cleavage and early growth.
In this connection it is interesting to note that
others have prepared an extract from sea-urchin eggs
and larvae which is growth-promoting, (91) and one
which is growth-inhibiting. As has also been found
BEGINNINGS OF CO-OPERATION 75
with goldfish, the growth-accelerating principle seems
to be associated with the protein fraction of the ex-
tract. When the whole extract is used, it is said to
be growth-inhibiting and to produce the same re-
sults as overcrowding. The point I have made is
that with the sea-urchin eggs, under the conditions
of our experiments, there is also an ill effect of un-
dercrowding, and that there is an optimum popula-
tion size for speedy development which is neither
too crowded nor too scattered.
Much similar work has been done with the ef-
fects of numbers on the rate of multiplication with
various protozoans. Again I shall have to select re-
sults from the mass of available evidence. The late
T. Brailsford Robertson (107) of Australia an-
nounced back in 1921 that when two protozoans of
a certain species were placed together, the rate of
division was considerably more than double that
which resulted with only one present. It should be
noted that during the time of these experiments and
in all these protozoa which we are considering re-
production was entirely asexual, by self-division of
the original animal. I subjected the data in Robert-
son's original paper to statistical analysis and found
that there were only thirteen chances in a thousand
of getting as great a difference by random sampling.
Such results must be taken seriously (Figure 10).
76 THE SOCIAL LIFE OF ANIMALS
They were. And the period after 1921 was en-
livened for some of us by denials from one first-
class laboratory after another that there was anything
significant in Robertson's data. Robertson himself
ISOLATED PAIRED
24 HOURS 20.5 92.4
RATIO 1 2.2
I 44
Wf
P = 0.0128
Fig. 10. Robertson found that when two protozoans
were placed together each yielded over twice as many as
when the same number of similar protozoans were iso-
lated.
rechecked and confirmed his results, though his ex-
planations of them tended to vary. For the moment
we are not concerned with the explanations; but
what are the facts? The first extensive corroboration
from outside Robertson's own laboratory came from
the work of Dr. Petersen at Chicago. When she cul-
tured the common Paramecium in small volumes of
liquid, she obtained the same results as had Rob-
ertson's critics, but when she used relatively larger
volumes of the same culture medium, a cubic cen-
BEGINNINGS OF CO-OPERATION 77
timeter more or less, she got an increase in division
rate with the presence of a second individual, as
Robertson had found it in the Australian form he
had studied.
Still the critics were not convinced. Accordingly
Dr. Johnson, now of Stanford University, repeated
this whole study using a different protozoan, one of
the Oxytricha. (68) When sister cells from pure-line
cultures were used there was no difference at the
end of the first day, whether the Oxytricha were in-
troduced singly or in pairs into one or two drops of
good medium. Later, the cultures started with one
organism always were ahead. With larger volumes,
two organisms showed a higher rate of reproduction
per original animal at the end of the first day than
if started with a single protozoan.
Again for larger volumes Robertson's results were
confirmed, and those of his critics for smaller vol-
umes. But Johnson had only started. He knew from
the work of others that if a protozoan is washed
through several baths of sterile water the associated
bacteria are rinsed off. Then if the washed protozoan
is put into a weak solution of the proper salts, into
which has been introduced known numbers of the
bacteria on which they normally feed, the problem
can be studied with a controlled food supply, both
as to kind and amount.
78 THE SOCIAL LIFE OF ANIMALS
This he proceeded to do. He found a common
bacterium on which his sterile Oxytricha would grow
NUMBERS OBTAINED IN 24- HOURS FROM THE
ISOLATION OF OXYTRICHA INTO CONSTANT VOLUMES
WITH DIFFERENT CONCENTRATIONS Of BACTERIA
CONCENTRN 4X 2X X X/4 X/lO
I
I
3.5 9.0 11.4 5.4 3.0
Fig. 11. The ciliate protozoan Oxytricha reproduces
more rapidly with a certain limited number of bacteria
present than with either more or fewer. (From Johnson.)
and reproduce faster than in the ordinary medium.
He made standard suspensions of these bacteria in
sterile salt solution, at what we may call an X con-
centration. The bacteria could reproduce little, if at
all, in the salt medium, so that he knew how much
BEGINNINGS OF CO-OPERATION 79
and what kind of fodder he was feeding his washed
protozoans.
The resuhs of varying the amount of food are
REPRODUCTION-RATE FOR 24 HOURS WHEN ONE OR TWO OXYTRICMA
ARE SEEDED INTO TWO DROPS OF P. FLUORESCENS
CONCCMTRN 4 X
seeoiNG t 2
8.0 tO.2 tO.6 10.4
Fig. 12. In the denser suspensions of bacteria the
protozoans divide more rapidly when cultures are inocu-
lated with two protozoans than if started with a single
individual. (From Johnson.)
shown in Figure ii. With X concentration, in
twenty-four hours one animal produced about eleven
progeny. With 2X concentration, isolated sister cells
produced nine, and with a 4X concentration other
isolated sister cells produced but three and a half.
The rate of reproduction also decreased when less
than X bacteria were present.
8o THE SOCIAL LIFE OF ANIMALS
Now he was ready for the grand Robertson test,
except that by this time nearly all the factors were
controlled. The results are shown in the following
figure (Figure 12). With X concentration it made
no difference whether he started his small cultures
with one or with two sterile animals. With 2X con-
centration, the cultures started with two individuals
did as well as in X concentration, but those which
were started with only one individual lagged defi-
nitely, producing only 80 per cent as many animals
in twenty-four hours. With 4X concentration even
the culture started with two Oxytricha was slowed
down, but not so much as that started with only
one. He had shown that in the presence of an ex-
cess number of bacteria, cultures seeded with more
than one bacterium-eating protozoan thrive better
than if but one is introduced. Not content with this
Johnson took another species and tried it all over
again with the same results.
From all this careful work we judge that the facts
on this particular aspect of the effects of numbers
present on the rate of asexual reproduction seem
now to be straight; but what about their expla-
nation? This, as it turns out, also interests us.
Robertson advanced the following hypothesis to
explain the results which he had observed. Dur-
ing division each nucleus retains as much as pos-
BEGINNINGS OF CO-OPERATION 8l
sible of an essential, growth-producing substance
with which it was provided, and adds to it dur-
ing the course of growth between divisions. At
each division, however, this substance is necessarily
shared with the surrounding medium in a propor-
tion that is determined by its relative solubility in
the culture water, and by its affinity for chemical
substances within the nucleus. The mutual speeding
of division by neighboring cells is due to each cell's
losing less of this necessary substance because of the
presence of the other. The more of this growth-pro-
moting substance there was in the cell, Robertson
thought, the faster would be the division rate; so
that any circumstance which would conserve the
limited supply would tend to speed up processes
leading to cell division.
Stripped to essentials this hypothesis says that as
a result of the presence of a second organism both
lose less of an unknown something which is essen-
tial for division than would happen if but one were
present. Returning to the problem after the criti-
cisms of half a dozen years, Robertson affirmed that
all the data and conclusions on the subject that had
been issued from his laboratory remained valid save
that they might apply to the ^ associated food or-
ganisms and not to the protozoans themselves.
Johnson has paid considerable attention to this
82 THE SOCIAL LIFE OF ANIMALS
problem, and has concluded that the results which
he has observed can be explained as due to bacterial
crowding; that the larger number of protozoans in-
troduced into dense cultures thrive best because they
are able to reduce the bacteria to density optimal
to the protozoa faster than their isolated sister cells
can; and therefore they show a higher rate of re-
production.
This does not seem to be the whole story; for from
points as distant as Baltimore (79) and Jerusalem,
(101) I have reports from trustworthy men that with
still simpler protozoans they are getting results which
suggest that some modification of Robertson's hy-
pothesis may be correct after all. These organisms
stimulate each other to more rapid growth merely
by their presence in the same small space.
With fine courtesy, Professor Mast of Johns Hop-
kins has placed a report of his experiments in my
hands in advance of publication and has permitted
me to summarize his results. He finds that popula-
tions of a flagellate protozoan grow more rapidly in
a sterile medium of relatively simple salts when
larger numbers are introduced than if the cultures
are started with only a few organisms.
I must not put too much stress on these reports,
pending the appearance of yet more data, but I
should expect to find here, as elsewhere, that com-
BEGINNINGS OF CO-OPERATION 83
plicated problems such as these that deal with the
rate of population growth are controlled by more
than one mechanism.
The suggestions from the simpler protozoans,
taken together with other aspects of the mass physi-
ology of protozoa which have been only partially
reviewed here, and with the acceleration of devel-
opment demonstrated for sea-urchin eggs, encourage
me to renew a suggestion made some years ago, (3)
which has, so far as I am aware, been overlooked
to date.
Let us go back to consider the case of external
fertilization among aquatic animals. When sperma-
tozoa and eggs are shed into sea water by sea-
urchins or other marine animals, their length of
life is distinctly limited. If a sperm fails to contact
an egg during the fertilizable period, death results
probably from starvation for the spermatozoa, per-
haps from suffocation for the egg. This means that
the animals of the two sexes must be fairly close
together if there is to be a union of the shed sexual
products. The most vigorous sperm of the sea-
urchin Arhacia can travel in still water about
thirty centimeters, that is, about one foot and two
inches. (55) Spermatozoa of these animals diluted
a few thousands of times can survive from three to
twelve hours; the majority succumb by seven hours.
84 THE SOCIAL LIFE OF ANIMALS
If a current catches it, such sperm can travel many
times thirty centimeters, but even in sea water the
sexes must be relatively aggregated if fertilization
is to be successful. In fresh water, the life of shed
gametes is much shorter. After ten minutes, eggs of
the pike lose the power to be fertilized, (102) and
the longevity of sperm of certain fresh-water fishes
is said to be less than a minute, so that in fresh
water the aggregation is even more essential. With
animals that require internal impregnation the
necessity for close co-operation between at least
two individuals is obvious. Such considerations must
be fundamental for the long-recognized breeding
aggregations of animals, especially of those that shed
eggs and sperm into surrounding water.
Mass relationships may be even more important
sexually, and here I come to the new suggestion:
perhaps they had a hand in shaping sex itself. Pre-
sumably sexual evolution started, as it does today in
plants, with a time when all gametes of any one spe-
cies were similar. Under these conditions a first step
toward the union of two reproductive elements
could be supplied by the greater well-being fos-
tered by the presence of more than one gamete
within a limited area, as even the simpler proto-
zoans are stimulated to asexual division today by the
near-by presence of another of the same species. In
I
BEGINNINGS OF CO-OPERATION 85
the survival value existing for separate living cells
before actual sexual union took place we can find a
logical beginning for the action of selection, which
would in turn, with present known values, result in
the establishment of the sexual phenomena as they
appear today. These fields have not been sufficiently
explored to allow for more than this flash of imagina-
tion, which future researches may verify or discard.
At this point it would be well to pause and look
back over the road we have traveled thus far. The
charts, (7) shown as Figures 13 A and B, show that
most of our evidence has come from fairly well down
among the simpler forms of life. I have called atten-
tion to mass protection of one sort or another among
bacteria, planarian worms, goldfish and the simpler
crustaceans. Actually there are in scientific literature
good cases of mass protection for almost all the ani-
mals shown in these charts; and where exact informa-
tion is lacking, as for example among the rotifers,
this is a result only of lack of interest in conducting
experiments on this point with these animals. I have
little doubt that we could, overnight, demonstrate
mass protection from colloidal silver for rotifers; but
we have more interesting work to do.
I have also shown active acceleration of fundamen-
tal biological processes as a result of numbers present
for sea-urchin eggs and larvae, and for various pro-
Bi(rdM M&mmalls
Amphil^ani^ /
.JZOA
oeba)
Ancesrral plants
ANCESTRAL CCELENTERATES
ANCESTRAL PROTOZOA "
Ancestral animal-plants — "^
Primitive protoplasm
Fig. 13. A recent suggestion concerning the ancestral
relations within the animal kingdom. The circles in A
B
CHORDATES
1^
ANCESTRAt COELENTERATES
ANCESTRAL PR0T02OA
Ancestral plants
Ancestral animal-plants —
Primitive Protoplasm
and B allow cross-identification. (From Allee in The
World and Man.)
88 THE SOCIAL LIFE OF ANIMALS
tozoans. These have been given in some detail, which
has not left time for similar demonstrations among
regenerating cells of sponges; nor have I time to tell
how hydra have been saved from depression periods
by the use of self-conditioned water. I have men-
tioned but not elaborated the fact that grouped ani-
mals frequently have different rates of respiration as
compared with their isolated fellows. This has been
recorded widely in the animal kingdom, notably
among planarians, certain lower crustaceans, some
starfish, fishes and lizards, and for some, at least, asso-
ciated survival values have been demonstrated. To
this extent, then, I have given the crucial evidence
I promised earlier that a sort of unconscious co-
operation or automatic mutualism extends far down
among the simpler plants and animals.
These charts should illustrate one other point. The
insects stand at the apex of one long line of evolu-
tion; mammals and birds are at the peak of another
line of evolution; the two have been distinct for a
very long time. This view of evolution indicates that
the ancestral tree of animals is not like that of a pine
tree with man at the very top and insects and all the
other animals arranged as side shoots from one main
stem. Rather, there are at least two main branches
which start low, as in a well-pruned peach tree. Both
rise to approximately equal heights, indicating cor-
BEGINNINGS OF CO-OPERATION 89
rectly that in their way the insects are as specialized
as the birds or mammals. Since both insects and
mammals have developed closely-knit social groups,
this is further evidence that there is a widely dis-
tributed potentiality of social life. We shall return
to this subject later.
IV
Aggregations of Higher Animals
A GREAT deal of skepticism is necessary in science,
if progress is to be even relatively steady and sound.
Not only must the scientist be skeptical of advance
reports of new results until he has seen the support-
ing evidence, no matter how stimulating the thesis
and how well it would explain material already
gathered; but in fields which lie near his own re-
searches it is necessary if possible to bring the prob-
lem into his own laboratory and there examine the
validity of the evidence itself. This repeating of ex-
periments in order to check the first observer is some-
times also a testing of scientific courtesy, but every
real scientist must be prepared to submit to it with
the best grace possible.
It is demanded also that from time to time one
should be skeptical of views long held, and of the
evidence on which they were built up, particularly
of the inclusiveness of the conclusions that have been
drawn. Without my own fair share of this skepticism
I should never have been drawn into what I knew
90
AGGREGATIONS OF HIGHER ANIMALS Ql
from the beginning would be a long and laborious
series of experiments concerning the effects of num-
bers present upon growth.
As long ago as the eighteen-fifties Jabez Hogg,
(62) an Englishman, found by experimenting that
crowding decreased the rate of growth of snails and
produced stunted adults. From that day to this there
has been almost no break in the reported evidence
that overcrowding reduces growth; the number of
reports that crowding in any degree increases growth
are relatively few.
This phenomenon has, however, been observed by
enough workers using animals widely distributed
through the animal kingdom to show that the retard-
ing effect of undercrowding on growth is real. Before
considering the implications of this statement let me
review briefly some of the evidence. (3) Here as else-
where I shall make no attempt to catalogue all the
available evidence; the list would be impressively
long but tedious.
It is relatively easy to show that mixed populations
of many animals grow faster than if the same number
of some one species are cultured together. The com-
mon experience of aquarium enthusiasts that the
presence of the snails in aquaria increases the rate of
growth and well-being of their fishes is a case in
point. Their rule-of-thumb experience has been fully
9^ THE SOCIAL LIFE OF ANIMALS
verified by careful laboratory experiments. A more
crucial test involves individuals of the same species:
all snails, let us say, or all goldfish. Is there some
optimum size of the population at which individuals
grow most rapidly?
For years I have been studying different aspects of
this problem with the aid of a succession of com-
petent, critical research assistants and associates. The
names of these young scientists are interesting and,
I think, important. They include Drs. Bowen, Welty,
Shaw, Oesting and Evans, and Messrs. Livengood,
Hoskins, and Finkel, all of whom have independ-
ently obtained the basic results I am about to de-
scribe. (13, 14, 76)
We have used goldfish for our experimental ani-
mals, because these are inexpensive, easy to obtain,
hardy under laboratory conditions, and able to stand
daily handling.
In order to have a consistently constant water we
make up a synthetic pond water by dissolving in good
distilled water salts of high chemical purity. Into
such water goldfish about three inches long are
placed in sufficient number so that they will give a
conditioning coefficient of about twenty-five. Let me
explain: this coefficient is obtained by multiplying
the number of fish by their average length in milli-
meters and dividing by the number of liters of water
AGGREGATIONS OF HIGHER ANIMALS 93
in the containing vessel. Living in this water the fish
condition it by giving off organic matter and carbon
dioxide. They are left in the water for twenty-one
hours or so, while a similar amount of the same water
stands near by under exactly similar conditions ex-
cept for the absence of fish.
At the end of this time the clean control water is
siphoned into a number of clean jars, and a small
measured goldfish is placed in each. At the same time
the conditioned water is siphoned, either with or
without removing particles (that is, of excrement,
etc.) that may be present, into similarly clean jars.
A set of small measured goldfish, like those used in
the control jars, are transferred into the conditioned
water. These small "assay" fish have been feeding
for about two hours before being transferred; the
larger conditioning fish are allowed to feed for a
somewhat longer time before being washed carefully
to remove food residues and replaced in another lot
of water to condition that.
Meantime the jars, 120 of them, are all washed
carefully; and after this is done the experimenter has
nothing more to do until the next day, except to put
the laboratory in order, keep the temperamental
steam distilling apparatus running, test the water
chemically in several ways, keep his records in order,
94 THE SOCIAL LIFE OF ANIMALS
and otherwise see that nothing untoward happens to
make him or anyone else question the results.
After some twenty, twenty-five or thirty days of
such care, in which Sundays are included, again each
fish is photographed to scale, as they were also photo-
graphed at the beginning of the experiment; the
photographs are measured and the relative growth
determined for the fish that have daily been placed
into perfectly clean synthetic pond water, as com-
pared with those which daily have been put into
conditioned water, that is, into the water in which
other goldfish have lived for a day.
During the course of an analysis of this problem
we have performed this simple basic experiment
many times. The first forty-two such tests involving
886 fish gave on the average about two units more
growth for the fish in the conditioned, slightly con-
taminated water, than for those in clean water (Fig-
ure 14). These results have a statistical probability
(P) of about one chance in a hundred million of
being duplicated by random sampling. Hence we
have demonstrated that under the conditions of our
experiments the goldfish grow better in water in
which other similar goldfish have lived than they do
when they are daily transferred to perfectly clean
water.
The problem that has been occupying us for some
AGGREGATIONS OF HIGHER ANIMALS
95
time is why this is so. What are the factors involved
that make this slightly contaminated water a better
medium for young goldfish than a clean medium?
We have said that the conditioning fish are fed
EfFECT OF SELF CONTAMINATED WATER ON GROWTH OF GOLDFISH
«0. 290 274
I
GROWTH 1.8 -0 2
no. 180 142
I
I
GROWTH 1.65 1.00
MO. 210 120
CONCErfTRATEO
I
I
GROWTH 2.28 t.ia
ma t6l 114
II
GROWTH 1.92
Ha 220 217
tl
GROWTH 2.59 2.20
Fig. 14. Goldfish grow more rapidly if placed in vari-
ous kinds of slightly contaminated (conditioned) water.
The numbers above the columns show the number of
fish tested. The longer column represents the growth in
conditioned water.
for two or more hours daily and are then washed
off and placed in a fresh batch of water. Although
the fish are never fed in the water they are condi-
tioning, within a few hours after their transfer into it
from the feeding aquarium the water becomes more
or less cloudy with regurgitated food particles. These
bits of food are large enough so that the growth-assay
96 THE SOCIAL LIFE OF ANIMALS
fishes can strain them out of the water. When such
particles are removed by filtering, the growth-promot-
ing power of the conditioned water is greatly les-
sened, but it is not completely lost. In our experi-
ments we found that suspended food particles ac-
counted for 80 per cent or more of the increased
growth in conditioned water over that given in clean
control water.
These experiments give certain suggestions con-
cerning some other conditioning factors that may be
acting. For example, we know that the skin glands of
fish secrete slime (Figure 15). When we have made a
chemical extract of this material we have frequently
recovered a growth-promoting substance, apparently
a protein, which was effective in stimulating growth
when diluted 1 to 400,000, or even 1 to 800,000 times.
At these dilutions it is not probable that this factor
is affecting growth by furnishing food material.
There are, of course, other possibilities, many of
which we have checked. The increase in growth is
not due, for example, to a change in the total salt
content of the water, for this does not change in our
experiments; nor to differences in acidity or oxygen,
nor, so far as careful quantitative analyses have re-
vealed, to changes in chemical elements present. We
may be dealing with some sort of mass protection,
such as was discussed in the last chapter, in which
J
AGGREGATIONS OF HIGHER ANIMALS 97
the conditioning fishes remove some harmful sub-
stance, but of this we have no real evidence.
Whatever the explanation, we are certain of the
facts, and we know that we have demonstrated a de-
EFFECT OF PROTEIN EXTRACT FROM SKIN OF
GOLDFISHES ON GROWTH OF GOLDFISH
NO. 56 59
EXTRACT
VS. ■■ P= 0.0106
CONTROL
.
GROWTH 1,95 0.54
NO. 61 122
EXTRACT
VS.
SALT CONTROL
GROWTH 3.22 0.61
P= 0.0006
NO. 26 28
EXTRACT
VS.
CONDITIONED
WATER
II
GROWTH 1.92 1.55
P= 0.26
Fig. 15. An extract from the skin of goldfish fre-
quently has growth-promoting power. The arrangement
of the figure is on the same plan as was used in Fig. 14.
98 THE SOCIAL LIFE OF ANIMALS
vice such that if in nature one or a few fish in a
group find plenty of food, apparently without will-
ing to do so they regurgitate some food particles
which are taken by others, a sort of automatic shar-
ing. Again, in water that changes rapidly, such stag-
nant-water fishes as goldfish, if present in numbers,
are able to condition their environment, perhaps by
the secretion of mucus, so that it becomes a more
favorable place in which to live and grow.
Perhaps I have lingered too long over this one
case; I am so close to the facts and to the tactics used
in collecting them that they may seem rnore interest-
ing to me than they will ten years hence. We have
run the same experiment with positive results with
a few other species of fishes; and we have also found
by experimentation that certain fish will regenerate
tails that have been cut off if several are present in
the same water more rapidly than if each is isolated.
(112) The same is true for the young tadpoles of sala-
manders, with which we have had experience. The
explanation of the more rapid regeneration of such
cut tails is probably relatively simple. The several
animals together more readily bring the surrounding
fresh water to approximately the salt content of the
cut and regenerating tissues than can be done by a
single animal placed in the same amount of water.
AGGREGATIONS OF HIGHER ANIMALS QQ
This may not be the whole of the story but it is prob-
ably a significant part of it.
In both of these cases the additional growth of
aquatic animals, which occurs as a result of the pres-
ence of other animals of the same species, is produced
in response to some sort of chemical which has been
given off into the surrounding water. This may be
nothing more than the unswallowing of surplus food
by the conditioning fish. With animals whose tails
have been freshly cut off the addition of salts to the
water by the group may balance the osmotic tension
at the cut surfaces and so favor re-growth. The excit-
ing result of these studies lies in the suggestion that
some less obvious growth-promoting substances may
also be secreted into the surrounding water.
Animal aggregations frequently produce physical
as well as chemical changes, and while we are con-
sidering the effect of numbers of animals present on
the rate of growth of individuals it is interesting to
examine one case in which growth-promotion appears
to have been produced largely by changes in tempera-
ture. Such an effect has been reported more than
once; it is most simply illustrated in a warm-blooded
animal, this time the white mouse. The experiment
was first performed in Poland, but the causal factors
were then only partially recognized. It has been re-
lOO THE SOCIAL LIFE OF ANIMALS
peated in our laboratory where significant steps have
been taken towards its further analysis.
Vetulani, the original experimenter, (117) used
closely inbred mice for his experimental animals. He
measured the growth of males and females separately
from the sixth and on through the twenty-second
weeks of their lives. After rearrangement he followed
them for ten weeks longer as a sort of control. Fresh
food was supplied in abundance each day, and proper
experimental conditions seem to have been main-
tained.
Growth during the first sixteen weeks of the ex-
periment is shown in the accompanying graphs (Fig-
ure 16). All started off at approximately the same
rate. After the fifth week of the experiment, however,
it is clear that the isolated mice were growing most
slowly, and they continued to do so as long as the
experiment ran. The most rapid rate of growth was
observed in those mice which were placed two to
four per cage; those five to six per cage grew next
best, and only slightly below these came those living
nine to twelve per cage.
Under the conditions of this experiment the iso-
lated young mice were most handicapped, those most
crowded were next, while those that were somewhat
but not too crowded grew most rapidly. When the
mice were rearranged for a continuing period of ten
OK — I 1 1 1 1 1 1 1 1 t I I I I . I
6 7 8 9 10 11121314 15 1G17 1819 20 2I22
A;,'c in weeks
Fig. i6. White mice grow faster in small groups than
in large ones; they grow slowest . when isolated (solid
line). (From Vetulani.)
102 THE SOCIAL LIFE OF ANIMALS
weeks the same relations held, showing that it was
the state of aggregation rather than individual dif-
ferences between mouse and mouse which was impor-
tant in producing the differences in growth rates.
Mr. Retzlaff, (105) the student who brought this
work into our laboratory, tried first to repeat Vetu-
lani's experiments in a room held at relatively high
temperatures (29-30° C). Under these conditions he
found that insofar as significant differences existed
they showed that most rapid growth occurred with
the isolated mice. When, however, he lowered the
room temperature to about 16° C. he obtained the
same general effect as reported by Vetulani. It would
seem then that in this case the opportunity to keep
warm in a chilling temperature is one of the main
factors in promoting growth of the crowded, but not
too crowded, animals. This conclusion is strength-
ened by recent analyses of the temperature relations
of mice, made by French physiologists, (30) which
show that a mammal as small as a mouse has great
difficulty in maintaining a constant temperature and
rarely does so for extended periods of time. A change
of external temperature from 30° to 18° C. will cause
a lowering of 0.4° in the body temperature of a
resting mouse.
With such temperature lability it is easy to see that
a few mice huddled together as is their habit could
AGGREGATIONS OF HIGHER ANIMALS IO3
help each other maintain their internal temperatures,
conserving energy for growth, while if isolated they
must use much of their energy in keeping warm.
Vetulani observed another factor at work. Some
of his mice had lesions of the skin which they treated
by licking. When these were in the head region they
could only be treated by another individual. Some
of his isolated mice had such lesions when at the end
of the first experimental period they were re-grouped
for further observation; these wounds were soon
cured by their new nest mates.
When one turns from studying the rate of growth
of individuals to that of populations of these higher
sexual animals, many of the same principles can be
observed working as were outlined in the last chap-
ter for the growth of asexual populations of proto-
zoans in which overcrowding retards population
growth, while optimal crowding, at least in many
instances, favors it.
With experimental populations of mice, for exam-
ple, three long, laborious experiments made in Scot-
land (36) and in Chicago (106) have indicated that,
under the conditions tried, the least crowded mice
reproduce most rapidly. The same holds true for the
well-studied fruit-fly, Drosophila. (96)
Neither with these flies nor with the mice is there
any indication to date of a more rapid rate of repro-
104 THE SOCIAL LIFE OF ANIMALS
duction per female when more than the minimal
pair is present. I have a strong suspicion, however,
that one would get a more rapid rate of increase per
number of animals involved if, instead of keeping
the sexes equal in numbers, there were a ratio, let
us say, of two females to one male.
We do know that with Drosophila the greatest
numbers are produced when the feeding surface is
relatively great but not too great; (60) this result may
be explained by the assumption that with too great
space, or in other words, with too few flies present,
wild yeasts or molds grow more rapidly than the
Drosophila can keep under control.
Another well-studied laboratory animal, the flour
beetle, Triholium, under certain experimental con-
ditions gives most rapid population growth at an
intermediate population size rather than with too
few or too many present. A study of data collected
by Chapman showed that in a flour beetle's little
world, a microcosm of thirty-two grams of flour, these
beetles, during the early stages of population growth,
reproduce most rapidly per female with two pairs
present (Figure 17). Reproduction is more rapid
when four pairs or even sixteen pairs are present,
than if there is only one pair. (3)
This work of Dr. Chapman's was done for another
purpose. We took it for an indication of possibilities.
AGGREGATIONS OF HIGHER ANIMALS IO5
and Dr. Thomas Park looked into the matter inde-
pendently. (88) He found the situation very much
as it had originally appeared to be. A Scotsman
named Maclagen had a curiosity along the same line
8
.
S^'^
/'
^N<
"§
/'
"^^^^^^
^6
Ji
\*^^>^^
\ ^^^^^^^^^
/'
\^ ^""X^
554
/
\ ^^frdays
^ 5
P
v..
i?
/'
*"'••. ^
2
//
""-..SSc/ays
1
1 « I 1 1
2 4 8 16 32 64
/nitiaC population per ^2 Sms, of f/oar
Fig. 17. Flour beetles reproduce more rapidly if more
than one pair is present.
and independently re-checked the whole matter with
the same results. (77) Three separate workers in
three different laboratories have now obtained essen-
tially similar results with these same beetles, and the
chances that all are mistaken are rather remote.
One of them, Dr. Thomas Park, has proceeded to
analyze the factors involved. (89) He finds that the
results come from the interaction of two opposing
tendencies. In the first place, adult beetles roam at
106 THE SOCIAL LIFE OF ANIMALS
random through their floury universe. They eat the
flour, but they may also eat their own eggs as they
encounter these on their travels. This habit of egg-
eating tends to reduce the rate of population growth,
the more so the denser the population.
The second factor is the experimentally proven
fact that up to a certain point copulation and suc-
cessive re-copulation stimulate the female Tribolium
beetles to lay more eggs, and eggs with a higher per-
centage of fertility. Thus the more dense the beetle
population the more rapid its rate of increase. The
interaction of these two opposing tendencies results
in an intermediate optimal population in which
more offspring are produced per adult animal than
in either more or less dense populations.
It may be felt that I have been keeping too closely
to the more or less artificial conditions found in the
laboratory. It is true that in an attempt to bring the
various aspects of the population problem under ex-
perimental control we have avoided those field obser-
vations which can only be recorded as more or less
interesting anecdotes. We have now come to a point
in our inquiry, however, at which it is necessary to
move directly into the field.
Given the evidence at hand, that optimal numbers
present in a given situation have certain positive
survival values and some definitely stimulating effects
AGGREGATIONS OF HIGHER ANIMALS 107
on the growth of individuals and the increase of
populations, we strike the problem of the optimal
size of a population in nature. This is an exceedingly
difficult question on which to obtain data. Suppose,
therefore, that we simplify it by asking what minimal
numbers are necessary if a species is to maintain itself
in nature?
This inquiry is a direct attempt to find under nat-
ural conditions the application of the statement by
Professor Pearl that "this whole matter of influence
of density of population in all senses, upon biological
phenomena, deserves a great deal more attention
than it has had. The indications all are that it is the
most important and significant element in the bio-
logical, as distinguished from the physical, environ-
ment of organisms."
Over and over again in the last half-dozen years
I have asked field naturalists, students of birds, wild-
life managers, anyone and everyone who might have
had experience in that direction, how few members
of a given species could maintain themselves in a
given situation. Always until this last summer I have
found that, stripped of extra verbiage behind which
they might hide their ignorance, the real answer was
that they did not know.
And then I had two pieces of luck; I found a man
and a scientific paper. My friend. Professor Phillips
lo8 THE SOCIAL LIFE OF ANIMALS
of South Africa, came to spend some weeks with us.
He told us that the Knysna Forest, a protected wood-
land in South Africa, has an area of 225 square miles,
fifteen miles on a side, and that this forest is the
home of a herd of eleven elephants, which can also
range outside the forest limits. On the other hand,
the Addo Forest, of twenty-five to thirty square miles,
supports a herd of twenty-four elephants. (98) Dr.
Phillips thinks that the smaller herd is not maintain-
ing itself, and that the larger one, under apparently
less favorable conditions as regards available area of
range, is at approximately the lower limit for keep-
ing up its own numbers. He estimates that an ele-
phant herd of about twenty-five individuals could
maintain itself in an unrestricted range providing
civilized man were absent.
He gave us a second example, of a herd of some
three hundred springbok on a protected reserve of
six thousand acres in the Transvaal, which was un-
able to maintain its numbers and became reduced
to eighty or ninety, on its way toward total ex-
tinction.
It is well known that in the life of equatorial
Africa the tsetse fly plays an important part. It carries
the trypanosomes which cause the deadly disease,
"sleeping sickness," of man and his domestic animals,
and which affect native game as well. The British
AGGREGATIONS OF HIGHER ANIMALS lOQ
colonial governments have been active in attempts
to control the density of these fly populations. In
general they are restricted to damp, low-lying forest.
In districts where this is confined to the borders of
water-courses, and hence where the fly belt has nat-
urally a definite limit and is restricted in size, an
ingenious fly trap has been used successfully. The
trap takes advantage of the natural reactions of the
tsetse fly. These are strongly positive to a slightly
moving dark object a few feet above ground. With
appropriate screening they can be caught as they fly
toward such an object; they will fly up and fall back
until they literally wear themselves out. It was at
first thought that such a trap would be helpful chiefly
in reducing the excess fly population; then, to the
delight of the control officials, they found that when
in these restricted fly belts the tsetse flies had been
trapped down to a certain minimum population
there was no need to catch the very last flies; below
the minimum level those remaining disappeared
spontaneously from the area. Nor did they return
unless brought back in considerable numbers accom-
panying movements of game, or as a result of the
slow extension of range from other infested areas.
The work of the control officials in such regions thus
was very much easier than had been anticipated.
Two pertinent cases concerning the minimum
no THE SOCIAL LIFE OF ANIMALS
number below which a species cannot go with safety
have come in part under my own observation. In
1913, my first summer at the Marine Biological Lab-
oratory at Woods Hole, Massachusetts, the veteran
scientists of the laboratory, at least those who still
were willing to exhibit naturalistic enthusiasms, were
greatly pleased at the visit of a flock of laughing gulls
to the Eel Pond near the laboratory. The main
breeding ground of these gulls is on Muskeget Island
off Nantucket. In 1850 the laughing gulls were abun-
dant there; but they were exposed to the depreda-
tions of egg takers and later, about 1876, to the
attacks of men interested in obtaining their striking
wings and other feathers to satisfy the millinery de-
mand for feathers of native birds, which was then
at its height. (49) Under this slaughter the colony
was nearly wiped out; at its low point about 1880
there were not more than twelve pairs of laughing
gulls left on Muskeget Island, and only a few of these
bred. A warden was employed in a somewhat extra-
legal capacity by certain ornithologists who regretted
seeing the species die out, and he was assisted by the
captain of the local life-saving crew in protecting the
gulls from raids. Later changes in laws regarding
protection of birds and the use of plumage in mil-
linery gave more secure protection for the growing
colony. For the first ten years the birds increased
AGGREGATIONS OF HIGHER ANIMALS 111
slowly, but thereafter more rapidly, until there are
now thousands breeding on the island, and their
range has spread to the mainland. In Woods Hole, at
the present time, these birds whose return in 1913
excited so much comment are as common as the
terns. In this case, a few breeding pairs, nesting in a
relatively safe place, were able to regenerate the local
population in less than fifty years; all that was needed
was protection from the predations of man.
The nesting colonies of gulls have attracted atten-
tion from many; a report by Darling has recently
appeared concerning certain relations between num-
bers of herring gulls in a colony and breeding be-
havior, and survival of young gulls on Priest Island
off the northwest coast of Scotland. (39) There are
indications that the members of larger colonies stim-
ulate each other to begin mating activities earlier
than when the colonies are smaller and, what is
apparently more important, there tends to be a
shorter spread in the time from the laying of the first
egg until the last one is laid. This means that the
breeding activities are more intense while they last.
The period between hatching and the growth of
the first adult plumage is a crucial time in the life
of young gulls. While they are in the downy stage
they are preyed upon by outside predators; also at
112
THE SOCIAL LIFE OF ANIMALS
this time the gull chicks that wander from their home
nests may be pecked to death by other members of
the colony. The toll of the chicks is comparatively
less, the shorter the time from the hatching of the
Survivor)
Time
Fig. i8. The "spread" of time in which eggs are laid
in a colony of herring gulls affects the percentage that
survive. The smaller the colony the longer the spread,
and the fewer survivors. [From Darling (39) by permis-
sion of The Macmillan Co.]
first fuzzy young gull until the last one changes to
a young fledgling with adult feathers. These relations
are graphically shown in Figure 18.
Darling thinks that the greater success of the larger
colonies does not lie in any vague factor of mutual
protection, but in the nearer approach to simultane-
ous breeding throughout the colony. This is a phase
of social facilitation which will be discussed more
fully in a later chapter.
These observations need to be extended and con-
AGGREGATIONS OF HIGHER ANIMALS 1 I 3
firmed. They suggest one mechanism, that of mutual
stimulation to mating, which may have operated to
produce social nesting among birds, and which seems
capable of giving added survival value to the larger
colonies, once the habit of collecting into breeding
flocks is established. We have here a suggestion that
these social colonies of birds have evolved far enough
so that there has come to be a threshold of numbers
below which successful mating does not take place.
The numbers that constitute this threshold probably
vary under a variety of conditions.
In one case, when only two pairs were present,
nests were built but no eggs were laid, while in a
more favorable season, with three pairs, eggs were
laid and one chick out of eight that hatched lived
through the downy stage.
I saw the laughing gulls myself at Woods Hole
last summer; and I also found a paper by Gross giv-
ing the case of another almost extinct population
which could not be revived. The heath hen, prob-
ably a representative of an eastern race of the prairie
chicken, was formerly very abundant in Massachu-
setts, and may have been distributed from Maine to
Delaware, or perhaps even further south. It was grad-
ually isolated by the killing of birds in the intermedi-
ate region and was driven back, until about 1850 it
was found only on Martha's Vineyard and the near-by
114 THE SOCIAL LIFE OF ANIMALS
islands, and among the pine barrens of New Jersey.
(56) By 1880, except for attempted and unsuccessful
introductions elsewhere, it was probably restricted to
Martha's Vineyard. In 1890-92 it was estimated that
one hundred to two hundred birds remained on that
island. Then several things happened at about the
same time: prairie chickens were introduced and
probably interbred with the vanishing heath hen,
protection of the birds was stiffened, and collectors'
prices went up! It is an interesting commentary that
most of the museum specimens, of which 208 are
known at present, were collected between 1891 and
1900, when the probable extinction of the heath hen
was noised abroad. This is one of the modern handi-
caps of small numbers; let a species or race become
known to be rare, and museum collectors feel it
their special duty to get a good supply laid in, just
in case it does become extinct.
By 1907, when the Heath Hen Association was
formed and employed a competent warden, the count
had been reduced to seventy-seven. Massachusetts
became aroused and purchased six hundred acres of
heath hen range and leased a thousand acres more.
The reservation was near a state forest which added
another thousand acres of protected range. The birds
responded to increased care and by 1916 it was esti-
mated that there were two thousand in existence.
AGGREGATIONS OF HIGHER ANIMALS 11 5
Then came a fire, a gale, and a hard winter, with
an unprecedented flight of goshawks, and in April,
1917, there were fewer than fifty breeding pairs. The
next year, when there was an estimated total popu-
lation of 150, the heath hen range was invaded by
several expert photographers who took motion pic-
tures of mating behavior. In the face of this disturb-
ance at a critical time, still a good year allowed the
birds to increase and again to spread over Martha's
Vineyard. In 1920, 314 were counted; but thereafter
a decline in numbers set in which was never stopped.
The figures for those five successive years are: 117,
100, 28, 54, 25. At this point extra wardens were put
on the job, who killed more cats, crows, rats, hawks,
and owls, the enemies of the heath hen. The next
year's count was 35; in 1927, there were 20; but in
1928, in a census that lasted four days, only a single
male was found. No other bird was seen thereafter,
though a reward of a hundred dollars was offered
for the discovery of another. This single male was
banded and released and was last seen alive on Febru-
ary 9, 1932. With his death the heath hen became
extinct. (18)
When this much is known of the decline in num-
bers of a given species there should be some knowl-
edge of the factors involved in its extinction. There
is. In the earlier years, as I have indicated with re-
Il6 THE SOCIAL LIFE OF ANIMALS
gard to museum collecting, there was undoubtedly a
considerable amount of poaching; but as population
of heath hens declined, local sentiment turned in
favor of protection and poaching decreased, both
because of a more intelligent public reaction to the
birds, and because of closer patrol by wardens. Dr.
Gross, whose account I have been following, thinks
that there was evidence of an inadaptability of the
species, an excessive inbreeding, and, at the end, an
excessive number of males. In such small populations
the sex ratios frequently become highly abnormal.
Disease and parasites took their toll. Predators, par-
ticularly cats and rats, were active. The females hid
their nests well and were faithful in remaining on
them, so that they were killed off by the fires which
at times whipped over the breeding grounds.
Over sixty thousand dollars was spent in trying to
save the heath hen, but without success. In contrast
to the laughing gull, which nested in a relatively
safe place and which came back from a population
as low as the heath hen's until the very last, this
unfortunate species was not able to adjust itself and
continue existence, even with as intelligent human
help as could be mustered in its favor.
The general conclusion seems to be that different
species have different minimum populations below
AGGREGATIONS OF HIGHER ANIMALS 1 1 7
which the species cannot go with safety, and that in
some instances this is considerably above the theo-
retical minimum of one pair.
By way of the laboratory, the coastal regions of
Massachusetts, and South African grassland and for-
est, we are arriving at a general biological principle
regarding the importance of numbers present on the
growth, survival and, as we shall see, upon the evolu-
tion of species of animals.
Lacking definitive information on this last phase
of the subject, we shall turn to mathematical explo-
rations of its possibilities, as made primarily by Pro-
fessor Sewall Wright. (127, 41) Although the ideas to
be presented are essentially simple in principle, they
are sufficiently novel and unfamiliar to challenge the
closest attention.
I shall not indulge here in the details of the mathe-
matical analyses, for the very good reason that I do
not understand them. If I were not convinced, how-
ever, that Professor Wright does understand them I
should not present this outline. It is only fair to say
that, in my opinion, in dealing with these ideal popu-
lations Professor Wright cannot bring into sharp
focus at one time all the factors that may be acting
in nature. This is what he Has been courageous
enough to attempt; the more nearly he succeeds, the
more likely is the calculation to be too complex for
1 1 8 THE SOCIAL LIFE OF ANIMALS
presentation in detail except to highly specialized
readers.
The environment is in a state of constant flux and
its progressive changes, whether slow or fast, make
the well-adapted types of the past generations into
misfits under present conditions. The result may be
rectified either by the extinction of the species, if it
is not sufficiently plastic, or through reorganization
of the hereditary types. In such a reorganization the
simple Lamarckian reactions apparently do not op-
erate; that is to say, when confronted with new,
critical conditions, species cannot go to work and
produce needed changes to order. The reactions are
much more complicated than that.
To present the modern interpretation of this re-
organization I need three technical terms which I
shall define before using. Genes are bits of proto-
plasm too small to be seen through the microscope,
which are located in all cells and which are thought
to be the bearers of heredity. They behave as indi-
visible units, that is to say, a gene if present in an
organism is either transmitted as a whole or not at
all. Gene frequency is the term applied to the fre-
quency with which a given gene is found in a popu-
lation, relative to the total possible frequency (two
in every individual). By mutation is meant a large or
small hereditary change which appears suddenly,
AGGREGATIONS OF HIGHER ANIMALS IIQ
usually in the sense in which I shall use it, as a result
of a change in one or more genes. With these three
terms in mind we are ready to try to understand how
the hereditary types may become reorganized.
Such a reorganization implies a change in gene
frequencies. By this I mean now that there will be a
decrease in the abundance of the genes which were
responsible for the past adaptations that are now
obsolete, and an increase in the frequency of those
genes which allow an adaptation to the new condi-
tions. Gene frequencies remain constant in a large
population unless changed by mutation, selection or
immigration. This is because of the unitary charac-
ter, without blending, and the symmetry of the
Mendelian mechanism of heredity.
These life-saving genes may have been present
in the species for a million years as a result of
long past mutations, without having been of any
value to the species in all that time. Now under
changed conditions they may save it from extinction.
It is important to note that organisms do not usually
meet changed conditions by waiting for a new muta-
tion; frequently all members of a species would be
dead long before the right change would occur. This
means that since a species cannot produce adaptive
changes when and where needed, in order to persist
120 THE SOCIAL LIFE OF ANIMALS
successfully it must possess at all times a store of
concealed potential variability.
I may interject parenthetically that at times this
appears to call for the presence of a considerable
number of individuals as a necessary condition to
provide the needed variations. A part of this reserve
of variability may be of no use under any circum-
stances; some characters may be useful, some may
never meet with the circumstances under which they
would have survival value; while others, though of
no use or even harmful when they appear, may later
enable the species to live under newly changed con-
ditions.
Hereditary changes tend to be eliminated as soon
as they run counter to decided environmental selec-
tion. In large populations the results of mutations
tend to stabilize about some average gene frequency,
which represents the interaction between the rate of
mutation and the degree of selection. Frequently
mutation pressure pushes in one direction and selec-
tion in another and the resulting gene frequency in
the population represents a point or zone of equi-
librium between these forces. In small populations
which are not too small, selection between genes
becomes relatively ineffective, and the gene fre-
quencies drift at random over a wide range about a
certain mean position. In very small breeding popu-
AGGREGATIONS OF HIGHER ANIMALS
121
lations, even though these may be small isolated
colonies of a large widespread species, gene fre-
quencies drift into fixation of one alternative or an-
other more rapidly than they are changed by selec-
CHANCE
I
0.5
LOO
Fig. 19. In small populations, genes drift into fixa-
tion or loss largely irrespective of selection; the fre-
quency of fixation or loss depends in the long run on the
relative frequency of mutation and reverse mutation.
(After Wright.)
tion or by mutation. Mutation, however, prevents
permanent fixation. The condition at any given
moment is largely a matter of chance.
Perhaps a diagram will help at this point. In Fig-
ure 19 the horizontal axis shows the different gene
frequencies in a population, and the vertical axis
gives the chances of the population under considera-
tion possessing any given gene frequency. At the left,
122 THE SOCIAL LIFE OF ANIMALS
the gene frequency is zero; that is, the gene in ques-
tion is absent from the population for the time being.
The height of the curve shows that there is a good
chance of this happening. At the extreme right the
gene has become fixed and all animals in the popu-
lation have it; they are a pure culture so far as this
gene is concerned. Again there is a high degree of
probability that this may happen when numbers are
few. But the intermediate condition, when the gene
is present in some but not all of the animals, shows
little chance of occurrence.
In such small populations, as has been said before,
the gene frequency is determined mainly by chance;
any given hereditary unit tends to disappear com-
pletely or become fixed and occur in all members of
the small inbreeding colony. Such a condition may
have been reached in the inbred population of the
heath hen on Martha's Vineyard.
With populations that are intermediate in size
there is a greater variety of possibilities. Some genes
are lost, others reach chance fixations, and others
fluctuate widely in frequency from time to time.
These conditions are shown in Figure 20.
If a given species is isolated into breeding colonies
in such a way that but little emigration occurs be-
tween them, a condition known to exist in nature, in
the course of time, as Professor Wright shows, the
AGGREGATIONS OF HIGHER ANIMALS 123
species will become divided into local races. This
will happen although at the time of separation the
populations were all homogeneous and the environ-
ment of all remains essentially similar.
If the environment does remain steady the larger
SELECTION
4
HUTATIOrt MUTATIOM
CHANCE
0 0.5 100
Fig. 20. In medium populations, gene frequencies
drift at random about an intermediate point but not so
much so that complete fixation or loss is likely to occur.
(After Wright.)
colonies will tend to keep the same hereditary consti-
tution as that which the whole species formerly had.
(Figure 21.) Small breeding colonies will, how-
ever, become pure cultures for different characters,
and it is impossible to predict the course of the
hereditary drift in any of these populations. As illus-
trated in Figure 20, the fixation will be a matter of
chance, and local races will result without any neces-
sary reference to adaptation.
The snails in the different mountain valleys of
Hawaii afford the classical illustration of this point.
124
THE SOCIAL LIFE OF ANIMALS
Each individual mountain valley has its separate
species of snails. They are distinguished by size, by
color markings, and by other characters which may
be wholly non-adaptive.
Colonies which are intermediate in size will pre-
UTATION
CHANCE
A
I
0 0.5 1.00
Fig. 21. In large populations, gene frequency is held
to a certain equilibrium value as a result of the oppos-
ing pressures of mutation and selection. (After Wright.)
serve a part of the variability that will be lost in the
smaller colonies. Even so, there will be some inde-
pendent drifting apart of the various gene frequen-
cies, so that these, too, will give rise to new local
races. Professor Wright's calculations show that with
mutation rates of the order of i:io,ooo or 1:100,000,
such intermediate populations, optimal for evolution,
will consist of some thousands or tens of thousands of
individuals.
With small breeding populations, then, genes tend
to become fixed or lost. Even rather severe selection
AGGREGATIONS OF HIGHER ANIMALS 125
is without effect. Individual genes drift from one
state of fixation to another regardless of selection. In
large populations, gene frequencies tend to come to
equilibrium between mutation and selection, and if
selection is severe, there tends to be a fixation of the
gene or genes that carry adaptive modifications, and
evolution comes to a standstill.
With a population intermediate in size, when there
are enough animals present to prevent fixation of
the genes on the one hand, but on the other, not
enough animals to prevent a random drifting about
the mean values determined by selection and muta-
tion, then evolution may occur relatively rapidly.
The results obtained will depend upon the balance
between mutation rate, selection rate, and the size
of the effective breeding population.
In one more case the effect of differences in sever-
ity of selection was worked out by Professor Wright
(Figure 22). With a moderate mutation rate, if the
selection is relatively weak, mutation pressure may
determine the result and the given character will
then drift to fixation or, as shown in the diagram, to
extinction. As selection pressures increase, selection
tends to take charge of the end products, and, if
slight, there is a wide variation about a mean; if
more intense, the amount of variation becomes less
and less.
126
THE SOCIAL LIFE OF ANIMALS
When a species is broken up into different breed-
ing colonies, as it is with the snails in the Hawaiian
fN5=80
Fig. 22. As intensity of selection increases it becomes
more and more dominant in determining the end result,
and the degree of variation is lessened; 4Ns gives selec-
tion pressure. (From Wright.)
valleys, (57) it can be similarly shown that the effects
produced depend on the rate of emigration between
colonies, as well as selection pressure, mutation pres-
sure, and population size, other factors being con-
stant. Cross-breeding introduces genes into a popula-
AGGREGATIONS OF HIGHER ANIMALS 127
tion in a way that is essentially identical with muta-
tion in its mathematical consequences; however,
similar results may be obtained in a much shorter
time by cross-breeding. And in fact all the different
results which have just been illustrated can be dupli-
cated by varying the numbers of the emigrants.
This is not the place to explore all the implica-
tions and possibilities of these interesting analyses.
The highly significant conclusion has been reached
that if a species occurs not as a single breeding unit
but broken into effective breeding colonies which
are almost isolated from each other, the members of
different colonies, given sufficient vigor, may evolve
into dissimilar local races. If one of these becomes
well adapted to its environment it may increase in
numbers and send out numerous emigrants. If these
emigrants find and interbreed with members of other
less advanced colonies they will grade these up until
they resemble the most adapted colony. This part of
the process resembles a stock breeder's grading up
of a mediocre herd of cattle by repeated infusions of
new and improved ''blood" into his herd. The sig-
nificant thing here is that the random differentiation
of local populations furnishes material for the action
of selection on types as wholes, rather than on the
mere average adaptive effects of individual genes.
The end results will vary even when the original
128 THE SOCIAL LIFE OF ANIMALS
population was homogeneous, and when mutation
rates are similar throughout, even though selection is
in the same direction in all parts of the different
colonies. The primary factor under these conditions
will be that of effective breeding population size, and
there will be greater chance for varied evolution
among the populations that are intermediate in size,
as contrasted with those which are small or large, and
still greater chance for evolution when a large species
is broken into small breeding colonies which are not
completely isolated from each other.
This argument, even as I have simplified it, is not
too easily followed the first time one goes over it.
Perhaps my use of an old teaching trick, that of repe-
tition of the same ideas with different words and
different illustrations, may be forgiven. In doing so
I am still leaning heavily on Professor Wright. The
series of diagrams shown in Plate IV are built on
one fundamental background. In perspective we see
two elevations, one higher than the other, and two
depressions which are the low points in a valley
between the two peaks. Every position is intended
to represent a different combination of gene fre-
quencies. The peaks represent gene combinations
which are highly adaptive; the depressions represent
those that lack adaptive value. The degree of adap-
tiveness is shown by the height occupied by the given
I#
€
o^
.X- O
clI
PLATE IV. A population originally possessed a set
of gene combinations of some slight adaptive value
(dotted line). With increased mutation rate it can ex-
pand to less adapted levels (A); with increased selec-
tion it contracts (B); if the environment changes the
gene frequency must shift (C); with small numbers
and close inbreeding the course of evolution is erratic
and extinction usually follows (D); with larger num-
bers, evolution takes place more readily (E); most read-
ily, when a large population is broken into local
colonies with inter-emigiation (F). (Modified from
Wright.)
AGGREGATIONS OF HIGHER ANIMALS 129
population. The variability of the population is
shown by the size of the area that is occupied. Every
individual in a species may have a different gene
combination from every other, and yet the species
may occupy a small region relative to all the possi-
bilities.
We may call the lower peak Mount Minor Adap-
tation and the higher one Mount Major Adaptation.
In Figure A we find a population which is fairly
well-adapted, but not so much so as if it occupied the
higher peak. Its original position and its variability
are shown by the dotted circle. As a result of increased
rate of mutation or of reduced selection, or both, the
variability of the population has increased and it
now spreads down to lower positions on this Mount
Minor Adaptation. It contains more aberrant indi-
viduals and even freaks than when subject to less
frequent mutation or to more severe selection, and a
freak may appear that is more adaptive; but this
important end has been achieved at the expense of
the variability which might have made a major ad-
vance possible.
Figure C introduces a different situation. As a
result of environmental change Mount Minor Adap-
tation has disappeared and the adapted population
has been able to move to a new location at about the
same level formerly occupied; now it is on the slope
130 THE SOCIAL LIFE OF ANIMALS
of Mount Major Adaptation, and if selection con-
tinues may be expected to move up that adaptive
peak. A continually changing environment is un-
doubtedly an important factor in evolution.
The effects of population size are illustrated in the
next three diagrams. The general background is the
same as in Figures A and B. In Figure D is shown
the effect of a decided reduction in population size,
and consequently in variability, in the species that
formerly occupied Mount Minor Adaptation. It is
in fact so small that selection has become ineffective
and the different hereditary qualities shift to chance
fixations. As non-adaptive characters become fixed at
random the species moves down from its peak over
an erratic, unpredictable path. With reduction of
population size below a certain minimum, control by
selection between genes disappears to such an extent
that the end can only be extinction.
With the species population intermediate in size,
with the same mutation and selection rates as before,
gene frequencies move about at random but without
reaching the degree of fixation found in the preced-
ing case. Since it will be easier to escape from low
adaptive peaks, the population will tend finally to
occupy the more adapted levels. The rate of progress
is, however, extremely slow.
Finally, in Figure F, we see the case of a large
AGGREGATIONS OF HIGHER ANIMALS 13I
species which has become broken up into many small
local races, perhaps as a result of restricted environ-
mental niches. Each of these local races breeds largely
within its own colony, but there is an occasional emi-
gration from one to another. Each tends, if it is small
in number, to give rise to different variations which
shift about in a non-adaptive manner. The total
number of relatively stable variations will be much
greater since the total number of individuals is so
much larger than in E. Under these conditions the
chances are good that some of the local colonies will
escape from the influence of Mount Minor Adapta-
tion and manage to cross the valley to Mount Major
Adaptation. Here the race will expand in numbers
and will send out more and more emigrants which
will interbreed with the stocks in the less adapted
colonies and tend to grade them all up toward a
higher adaptive level.
The conclusion is as Professor Wright says: "A
subdivision of a large species into numerous small,
partially isolated races gives the most effective setting
for the operation of the trial and error mechanism
in the field of evolution that results from gene com-
binations."
In the rate of evolution, therefore, population size
is as important as we have seen it to be in the growth
1S2 THE SOCIAL LIFE OF ANIMALS
of individuals or in the gTO\\ih of popnlation num-
bers: and the optimal population size does not coin-
tide \sith either the largest or smallest possible but
lies at some iiuermediate point.
V.
Group Behavior
IN THE second chapter I told of how I stumbled on
the fact that in the breeding season the normal be-
havior of isopods is affected by numbers present.
Such effects have long been known for many types
of behavior, and it would not be profitable here to
catalogue and analyze all the cases that are on record.
Rather, as before, I shall select certain well-authenti-
cated examples of breeding reactions and of other
types of behavior. Those which are chosen are espe-
cially noteworthy because of the behavior pattern
which is involved, or because freshly observed, or
both.
And here is a shift in emphasis. I have been stress-
ing the existence of a widespread, fundamental auto-
matic co-operation which has survival value, and have
given evidence that it is a common trait in the animal
kingdom. In this chapter I shall discuss group be-
havior which may or may not have immediate sur-
vival value. In each instance, and throughout the
discussion as a whole, I shall be engaged in trying
133
154 THE SOCIAL LIFE OF ANIMALS
to find to what extent behavior is influenced by the
presence of others, and shall not consistently attempt
to assay possible values which may or may not be
involved.
With many more or less social animals the group
up to a certain size facilitates various types of be-
havior. This is frequently called social facilitation.
Shore Line
Fig. 23. Manakin males establish rows of mating courts
in the Panamanian rain-forest. (From Chapman.)
One phase of social facilitation is illustrated by some
observations of the mature student of birds, Frank E.
Chapman, (28) near the tropical laboratory on Barro
Colorado Island in the rain-forest of Panama. Mr.
Chapman found that males of Gould's manakin
establish lines of courting places (Figure 23). The
manakin is a small warbler-like bird, delicately
colored and relatively inconspicuous. Each of the
courting places is occupied by a single male; the line
thus formed extends for many yards through the
undergrowth of the rain-forest. From time to time
each day during the long nesting season, the males
resort to their individual cleared spots on the forest
GROUP BEHAVIOR 1 35
floor and make their presence known by a series of
snaps, whirrs and calls which may be heard as far as
three hundred yards. The females, who are more
quiet and retiring, apparently are attracted by the
line of males; they come individually from the sur-
rounding thickets and each mates with one of the
males. The evidence suggests that they are attracted
from a greater distance by the spaced aggregation of
males than they would be by isolated courting places.
The more or less organized line of males in breeding
condition apparently facilitates the mating of these
jungle birds.
This is a highly specialized example of the wide-
spread phenomenon of territoriality which can be
recognized even among breeding fishes, (103) and
which has been much studied of recent years in birds.
(65) Typically the male birds arrive first in the
spring and take up fairly well-defined territories in
the same general area, which they defend from in-
truding males. Then the females come in and flit
from territory to territory before settling down to
raise a brood with one particular male. There is
always the strong suggestion that the presence of a
number of singing males, even if spaced about in
different territories, attracts and hastens the accept-
ance of some one of them by an unmated female.
Group stimulation of the amount of food taken
136
THE SOCIAL LIFE OF ANIMALS
has been reported for various animals, including
rats, (59) chickens (23) and fishes. (118) I shall illus-
trate by some of the experiments conducted in our
laboratory by Dr. J. C. Welty. These have been
150
125
a
te.
s:ioo
^ 75
<
<
o
u.
o
le 25
la
<0
E
C
• GROUPS OF FOUR
O ISOLATED
DAILY FEEDmS 5
Fig. 24. Many kinds of fishes eat more if several are
present than if they are isolated. (From Welty.)
amply verified by other research workers. In connec-
tion with experiments on the effect of numbers on
the rate of learning in fishes, which will be discussed
later. Dr. Welty undertook to find whether grouped
fish ate more or less than if they were isolated. The
results of a typical experiment are illustrated in
Figure 24.
Goldfish were photographed to scale, and those of
GROUP BEHAVIOR I37
similar size were selected for experimentation. Two
groups of four each were placed in separate crystal-
lizing dishes and eight others were isolated each into
a wholly similar dish. The different dishes were sep-
arated by black paper so that vision from one to the
other was impossible. A known number of the small
crustacean, Daphnia, were introduced daily into each
dish. These living Daphnia had been screened so as
to select the large animals only. As shown by the fig-
ure, fish in all groups of four ate decidedly more on
the first three days of the experiment. At this time
the two lots were shifted. Those that had been
grouped were now isolated, and vice versa. There
was an immediate shift in the numbers of Daphnia
taken, with the newly isolated animals now eating
less than the accompanying groups. This indicates
that we are dealing with an effect of numbers present
rather than with chance differences in individual
appetites. This difference kept up steadily until the
last three days of observation, when an interesting
complication arose. By this time the grouped fish
were receiving a total of over six hundred Daphnia
daily, including those which were eaten and the
extras added to insure an economy of plenty. Each
isolated fish was receiving only one-fourth as many.
Now six hundred and more large Daphnia, each
about an eighth of an inch long, make quite a swarm
9,8 THE SOCIAL LIFE OF ANIMALS
in a none-too-large crystallizing dish. The consump-
tion of food per animal by the grouped fish fell off,
and as was shown by appropriate tests, this was due to
the action of a so-called confusion effect. When fewer
Daphnia were present, a fish might be observed to
swim after an isolated crustacean and eat it, whereas
a dozen Daphnia or so in the immediate field of
vision seemed to offer conflicting stimuli that blocked
the feeding response. Working on this suggestion,
one group of four was given the usual quota of some
six hundred Daphnia all at once; another group was
given only one hundred at a time, and when these
were approximately all eaten then another hundred
would fjc introduced, and so on until the end of the
regular feeding period. This prevented the Daphnia
from being too dense at the beginning of the hour's
feeding time. The isolated fish were fed as usual.
Under these conditions the grouped goldfish which
were fed one hundred Daphnia at a time ate defi-
nitely more than those given the whole confusing
mass at once.
Here we come upon two, not one, mass effects. In
the first place we see that the fish in groups of four
were stimulated to eat more food than if isolated,
and this depended on their state of aggregation. But,
incidental to this demonstration, we hnd that in the
presence of too many animated food particles a con-
GROUP BEHAVIOR 1 39
fusion effect arises which decreases the feeding effi-
ciency of the fish.
It has been suspected for years that such a confu-
sion effect exists and has survival value for small
animals flocking together in the presence of a preda-
tor, such as small birds in the region of a hawk.
These observations of Welty's make the best demon-
stration that I know of the existence of such an
effect, in this case the Daphnia in the presence of the
fish. I am less interested in this confusion effect at
present than in the demonstration of social facilita-
tion in feeding, a phenomenon which has been
shown to exist for a number of fishes, including zebra
fish, paradise fish, goldfish and guppies of the more
usual aquarium varieties, and the lake shiner, No-
tropis atherinoideSy as well.
None of these fishes is very social, that is, none
of them group into close schools. For evidence of
similar social stimulation among social animals it is
interesting to examine the effect of numbers present
on the digging behavior of the highly social ants.
The account of this work was published in 1937 by
Professor Chen of Peiping, China. (29)
These ants, a species of Campanotus, dig their
nests in the ground. It was found that all the worker
ants of this species are capable of digging a nest
when in isolation, but that the rate of work varies
140 THE SOCIAL LIFE OF ANIMALS
with different individuals. If marked ants, whose
reaction time has been tested in isolation, are placed
together in pairs or in groups, they will start work
sooner and will work with greater uniformity than
if alone.
With oriental patience. Professor Chen and his
assistants collected and counted the number of the
tiny pellets of earth which were dug by different
individual ants when isolated, and when members
of groups of two or three ants. They found that the
number of pellets removed is greater when the ants
work in association with others than when each
works alone. This accelerating effect is greater for
slow than for rapid workers; when ants with inter-
mediate working tendencies were tested (Figure 25)
they were found to be speeded up when in com-
pany with a rapid co-worker and relatively retarded
when placed with a slowly working ant. Interestingly
enough, there was no difference between the stimu-
lating effect of one additional ant and of many ants
on the rate of work of a given individual. The social
facilitation seemed maximum for these digging tests
when only a second individual was present.
Ants which regularly work rapidly were found to
be physiologically different from those that work
more slowly. The faster workers were more suscepti-
ble to starvation, to drying, and to exposure to ether
0 5 ra e 20 25 30 35 40 45 50 55 60 5 10 15 20 25 30 35 40 45 50 55 60
TIME IS MINUTES
Fig. 25. An ant which works at an intermediate rate
(Ml) may be speeded up if placed with an ant which
works more rapidly (Rl) and slowed down if put with a
slower worker (SI). (From Chen.)
142 THE SOCIAL LIFE OF ANIMALS
or to chloroform. Tests that have been made by
others indicate that animals that are more active
physiologically usually succumb sooner under such
adverse conditions, just as these rapidly-working ants
were found to do. These are exceedingly interesting
results because here we see that ants with apparently
innate differences in speed of fundamental processes
are affected in their speed of digging by the presence
or the absence of a nest mate. The ant of intermediate
speed, presumably with an intermediate underlying
reaction system, is most interesting of all, because it
can be either speeded up or retarded according as it
is placed with an active or a more passive individual.
In this connection it has been known for over a
decade scientifically what was common sense before
that time, namely, that human animals, whether
adults or children, can accomplish more mental and
physical work, at least of certain kinds, and will work
with greater uniformity when in association with
others doing similar tasks, than if obliged to work in
isolation. (15, 84)
Such considerations lead directly to problems con-
cerning the effect of numbers present on the rate of
learning in man. Here we find a set of questions that
have great and immediate human significance. The
world over, the training of the young animals of
their own species is one of the major preoccupations
GROUP BEHAVIOR 143
of mankind. This is particularly true in the United
States, where we are engaged in mass education on
an unprecedented scale. This teaching of the young
to the extent to which we are attempting it is an
expensive business in time, in effort and in money.
We need to know, therefore, the number of these
interesting young animals that can be trained to-
gether with best results. In other words, what is the
optimal class size for the various levels of training
from pre-school days through the preparation for
the doctor's degree and further?
In part, the proper answer to this question calls
for a statement of educational objectives. The devel-
opment of strong individuality, for example, is not
necessarily accomplished by the same teaching meth-
ods and class size which favor the growth of conform-
ity to group patterns; and the rapid development of
mastery of so-called skills may call for difiEerent num-
ber relations than those needed for the mastery of
logical thought.
Even without positive information we can guess
that the tutorial method with individuals or very
small groups will best serve some ends while others
will be achieved most readily in larger groups. The
question, or a simplified part of it, thus becomes:
What class size favors optimal rate of learning of the
usual class material presented at different ages?
144 THE SOCIAL LIFE OF ANIMALS
As might be anticipated, the difficulties of human
experimentation being what they are, it is hard to
collect accurate information on this point. Much
depends on the comparative accuracy of the sam-
pling, and also on more subjective factors, such as
the attitude of the teacher and of the students toward
large and small classes. There is also a factor which I
have not seen mentioned in the literature on the
subject, the effect on the student of realizing or sus-
pecting that he is an object of experimental interest,
an educational guinea pig. This stimulus is more
likely to be potent, in my opinion, when the student
is a member of a class which is unusual in size.
In the more careful studies, results of which have
been published, the class numbers have ranged from
"small" through ''medium" to "large." The "small"
experimental classes apparently have about twenty
to twenty-five members; this represents a more usual
experience to the student, and he is more likely to
be conscious of class size when he is a member of a
large class of seventy-five or more than when he is in
a small class or a medium-sized one of thirty-five to
forty. The sizes that are counted "large" or "small"
vary greatly, sometimes in the same experimental
treatment, so that frequently the comparisons are
between larger and smaller classes, both medium in
size, rather than between real extremes in numbers.
GROUP BEHAVIOR I45
Frequently, too, the teaching practice varies in
the two classes. Thus in one experiment the smaller
classes in high-school geometry contained about
twenty-five, while the large ones had about one
hundred members. In the large classes a student
helper was present for every ten class members.
These helpers were superior students in geometry of
the preceding year. As nearly as I can discover, there
were no student helpers in the small classes. Under
the conditions it is perhaps not unexpected that a
better showing was made by those in the large classes.
With them, there were present not only more in-
structors per student but these were people of nearly
their own age, who could be approached without
hesitation not only in class but out of class and even
out of school hours. Every mature teacher knows
that even with the best intention and the most demo-
cratic attitude, age differences widen the gap between
the teacher and the taught, whatever other compen-
sations there may be.
The most comprehensive experiments I have seen
reported in this field are those of the sub-committee
on class size of the committee on educational re-
search at the University of Minnesota. (66) These
were carried on at the college level and involved 109
classes under twenty-one instructors in eleven de-
partments of four colleges in the University of Min-
146 THE SOCIAL LIFE OF ANIMALS
nesota. Forty-two hundred and five students were
observed in large classes, and 1,854 in small ones;
of these 1,288 were paired as to intelligence, sex
and scholarship before the experiment began. One of
each pair was assigned to a large and one to a small
class in the same subject taught by the same instruc-
tor. In this way the obvious variables were controlled
as well as is humanly possible, unless we could have
a large number of identical twins with which to
experiment.
In 78 per cent of the experiments a more or less
decided advantage accrued to the paired students in
the large classes, and at every scholarship level tested,
the paired students in the large sections did better
work than their pairs in the smaller ones; the excel-
lent students appeared to profit somewhat more from
being in large classes than their less outstanding
fellows.
Of the available data, a re-examination of the sum-
maries indicates that there is on the average a dif-
ference in the means in the final grade of 4.1 points,
favoring the students in the larger classes. There
is a statistical probability of matching this by
random sampling of four chances in ten million
(P = 0.0000004), and this despite the fact that the
majority of the class comparisons did not give signifi-
cant differences when considered alone.
GROUP BEHAVIOR I47
The numbers in the smaller classes usually ranged
from twenty-one to thirty, but in some classes
dropped as low as twelve; in the larger classes there
were usually thirty -five to seventy-nine students; in
the largest, one hundred and sixty-nine. Under the
conditions which prevailed in these classes in psy-
chology, educational psychology and physics, the stu-
dents in the larger class sections made slightly but
significantly higher final grades than those in smaller
sections of the same subject taught by the same
instructor.
So much for objective experiments. It happens
that subjective estimates, made both by teachers and
by students at Minnesota, favor the smaller rather
than the larger classes. It was even true that the
students were better satisfied with the marks re-
ceived in smaller classes than they were with the
slightly higher grades given them in the larger sec-
tions.
The general attitude seemed somewhat like that
toward a friend of mine who teaches general mathe-
matics at Purdue University. He is an experienced
and excellent teacher. His program for one semester
required that he should meet a normal-sized class
of thirty to thirty-five at eight o'clock, and that at
nine o'clock he should meet a class of double the size
in a larger room, to repeat the same subject matter.
148 THE SOCIAL LIFE OF ANIMALS
At the close of the semester the two sections were
asked to rank the instructor on many different points.
Uniformly the students in the larger section rated
him lower than those in the smaller section, in such
matters as teaching skill, pleasantness of voice, neat-
ness of appearance and personal attractiveness!
I have had a fairly extensive teaching experience,
which has included work in grade- and high-school
teaching, as well as over twenty-five years of teaching
at the college and university level, during which time
I have taught classes of almost all sizes, from those
of over six hundred at the University of California
to the graduate classes of three or four that come my
way; and I must confess to a personal prejudice
against these very large classes. Even when using the
same lecture notes, I do not give the same lecture to
five hundred students that I give to forty or fifty.
On the other hand, even with graduate classes and
advanced seminars I am prejudiced in favor of hav-
ing enough students, which means at least eight to
ten, to give a certain esprit de corps to the group.
Such personal opinions have their value, particularly
when they click with experimental results such as
those outlined by Hudelson from the experiments
at Minnesota. It is unfortunate that those experi-
ments did not test either the upper or the lower
limits of class size which are conducive to good class-
GROUP BEHAVIOR I49
room performance on the part of the students; and I
know of none that does test these points adequately.
Some of the difficulties which are inherent in ex-
perimentation on the effects of class size on the rate
of learning in man can be obviated by the use of
non-human animals. This procedure does not solve
all the requirements for elegant objective experimen-
tation, and has the additional real difficulty of elim-
inating all possibility of adding subjective impres-
sions to objective findings, a point which makes one
of the strongest arguments for experimentation on
man when feasible.
In some respects the most completely controlled
experiments on the effect of numbers present on
the rate of learning are those that Miss Gates and I
performed some years ago, using common cock-
roaches as experimental animals. (52) Earlier work
by two independent investigators had shown that
cockroaches can be trained to run a simple maze,
and can show improvement from day to day. In our
experiments we found that the cockroaches could be
trained to run the maze we used by fifteen to twenty-
five successive trials on a given day, and showed defi-
nite improvement both in time taken to run the
maze and in number of errors. However, unlike the
experience of our predecessors, these University of
150 THE SOCIAL LIFE OF ANIMALS
Chicago cockroaches could not carry over the effects
of training from one day to the next.
The reason for this difference between our cock-
roaches and those around St. Louis and in Germany
is not known. It may be that at the University of
Chicago, despite our reputation for scholarship, the
local cockroaches have a low IQ, or it may be that
since we used animals from the bacteriological lab-
oratory, because of their unusual size and physical
vigor, we were unconsciously selecting the dumber
sort. Or perhaps, contrary to our plan, we set them a
problem which is intrinsically more difficult for the
cockroach mentality. In any event, it is important to
remember that our cockroaches forgot overnight any-
thing they may have learned the day before. As it
turns out, this was fortunate for the experiments we
were carrying on, because we could match up indi-
vidual cockroaches with the same speed of learning
in pairs or groups of three for later tests without fear
of a carryover from their previous experience.
The maze used is shown in Figure 26. It consisted
of a metal platform from which three runways ex-
tended, each about two inches wide and a foot or so
long. The two side runways ended blindly, but the
center one led to a black bottle, which allowed the
cockroaches to escape from the light. This apparently
GROUP BEHAVIOR I5I
was a reward for cockroaches which, when possible,
give a negative reaction to light.
The three-pronged set of runways was mounted
about half an inch above a pan of water, which the
majority of the cockroaches tended to avoid, and so
kept on the runways. The tests were all made in a
Fig. 26. A simple maze used in training cockroaches.
dark room and light was furnished by a single elec-
tric bulb mounted just above the point where the
central runway left the main platform. In other
words, the cockroaches, which are negative to light,
had to learn to run through the area of strongest
illumination in order to reach the dark bottle which
served as a reward. After two minutes' rest in the
dark bottle the cockroaches were literally poured out
onto the platform of the maze without being touched
by the experimenter, and observation of them began
again.
The problem as set was about at the limit of cock-
152
THE SOCIAL LIFE OF ANIMALS
roach ability. Approximately one-third of the insects
tested never learned to stay on the maze; whenever
they were placed on it they proceeded immediately to
run off into the underlying water. Of the two-thirds
n
16
15
14
13
12
U
9-
8-
isoIa."tecL *
paired
J roup of 3
\
I
15
Trials
— r-
20
25
Fig. 27. Isolated cockroaches make fewer errors on
the maze than the same animals paired, and still fewer
than if three are being trained together.
GROUP BEHAVIOR
153
that did learn to remain on the maze, a half, or an-
other third of all those tested, did not show improve-
ment in speed of reaching the bottle, after repeated
12-
isola-tecL •— *
U-
paired
^roup of 3 •—•
10-
9-
8-
0 7-
t (>■
c
f 5-
\
\
A-
>s^^^
3
^ .
2-
1-
10
15
Trials
20
25
Fig. 28. They also take less time.
trials. Thus only one-third of the cockroaches we
tested showed improvement with experience, and,
as I said before, they forgot overnight all that they
learned during the day.
As shown in the summarizing graphs (Figures 27
and 28), isolated cockroaches made fewer errors per
trial throughout the whole training period. They
154 THE SOCIAL LIFE OF ANIMALS
also took less time to run the maze than when the
same animals were members of pairs or of groups of
three. Turning the comparison around, paired cock-
roaches took longer time per trial and made more
errors than when isolated, and groups of three took
still longer and made more errors than those in pairs.
A study of the rate of improvement shows that
during the early part of the training, as is indicated
by the slant of the graphs, so far as time spent is
concerned, paired cockroaches improved more rap-
idly than they did if isolated or in groups of three,
and those placed three together on the maze im-
proved somewhat more rapidly than they did when
isolated. Thus, while the presence of one or two extra
cockroaches slowed down the speed of reaction on the
maze and increased the number of errors made at all
times, yet the rate of improvement in speed of re-
action was higher when more than one was present.
There was, however, no significant difference in rate
of improvement as measured by number of errors.
Excluding this one aspect of rate of improvement
in time spent on the maze, in all other phases of
the experiment isolated cockroaches turned in a bet-
ter learning performance than they showed when
more were present. Evidently under the conditions
of our experiments the tutorial system usually works
best with cockroaches.
GROUP BEHAVIOR 155
Essentially the same sort of experiment was tried
with isolated and paired Australian parrakeets, which
are commonly called love birds. (11) Rather naively,
perhaps, I thought that since these birds so readily
pair off, perhaps two might learn to run a simple
maze more rapidly than a single individual would.
This turned out to be entirely a mistaken idea. I
shall spare you the details concerning this maze; it
was adequate in size, so that two birds could pass
through practically abreast. Almost all the ninety-
odd birds that were tested learned easily to run the
maze and normally reduced their time per trial from
about two minutes to a few seconds, after six or
seven days of training. Errors also were reduced, and
several of the birds were trained so that they ran
the maze day after day with no errors at all.
The selected summarizing graphs (Figures 29 and
30) will outline the results obtained. It made no dif-
ference whether the birds were caged in pairs or
separately; if placed alone in the maze the perform-
ance was similar. If, however, two birds were put
together in the maze, the speed was reduced and
errors increased as compared with the scores made
by isolated parrakeets. It made no difference whether
two males, two females or a male and a female were
trained in the maze together; there was always in-
terference. The tendency was for the more rapid
156 THE SOCIAL LIFE OF ANIMALS
bird to slow down rather than for the slower bird
to speed up. The paired birds tended to take the
same time and to make the same errors. Given suf-
ficient training, they might make perfect scores so
Trials
Fig. 29. Parrakeets learn equally well if trained when
isolated, whether they are caged singly or in pairs. A,
time per trial; B, errors per trial.
GROUP BEHAVIOR
157
far as errors were concerned, but even after long
training the performance of pairs was always more
Fig. 30. Parrakeets learn more rapidly if trained
alone than if two are placed together in the maze. A,
time per trial; B, errors per trial, (The upper curve is
unsmoothed; the lower three have been smoothed mathe-
matically.)
erratic than that of isolated birds. When birds that
had been trained to a consistent level of excellence
were exchanged so that those formerly isolated were
paired and those formerly paired were isolated, their
behavior in the maze took on the characteristics
158 THE SOCIAL LIFE OF ANIMALS
usually shown by paired and by isolated birds, prov-
ing that the type of reaction given was a result of
the numbers present rather than of the working of
other factors. With these love birds then, contrary
to the original assumption, all indications were that
being paired in the maze slowed down the rate of
learning and increased the erratic character of their
behavior.
Our experience with the general problem did not
end here. I teach at the University of Chicago a
favorite course called Animal Behavior. In this class
the beginning research students attempt some small
problem and frequently make good progress toward
its superficial solution. One of these student projects
has been the training of the common mud-minnow
to react to traffic lights. The fish were trained to
jump out of water and obtain a bit of earthworm
when red was flashed. Under the green light they
were conditioned to retire to one of the bottom cor-
ners. If they did jump under green light they were
fed filter paper soaked in turpentine. Within two
months a lot of fishes, isolated one in each small
aquarium, could be trained so that they would have
been given an A for the project if they had been
properly enrolled students.
When, however, several fishes were placed together
in the same aquarium and an attempt was made to
GROUP BEHAVIOR 159
train all at the same time the rate of learning was
retarded. Paired fish reacted as well as if they had
been isolated, but the reactions of groups of four
were slowed down, and those of ten even more so.
Two fish would rarely jump at once, and when some
one individual was getting set to jump for the food
under the red light, another would frequently come
along and give him a jab in the belly which would
stop all tendency to jump for the time.
One more instance remains to be reported. Dr.
Welty, who has been mentioned before, undertook
to train goldfish to move forward from the rear
screened-off portion of an aquarium through a door
into a small forward chamber where each was fed
just after it came through the opening. (118) An
aquarium-maze, similar to those used, is shown in Fig-
ure 31. The signal to the fish that it was time to
react came from increasing the intensity of light in
the aquarium and opening the door between the two
compartments. Under Dr. Welty's careful coaching
the fish improved rapidly in their speed of reaction
and usually had reached a good level of performance
by the sixth day of training.
In his experiments almost a thousand fishes were
trained at one time or another. The results of a
sample experiment are recorded in Figure 32. In this
test there were eight goldfish, each isolated in indi-
i6o
THE SOCIAL LIFE OF ANIMALS
vidual aquaria, four sets of paired goldfish, two lots
of four placed together, and one group of eight in
one aquarium. As shown by the graph, there was a
Fig. 31. Feeding a fish which has just come through
the opening from the larger side of the aquarium. (From
Welty.)
marked group effect on the rate of learning. The
speed of first performance of the untrained fishes was
most rapid with eight present and slowest with iso-
lated goldfish. In the early days of rapid learning the
same order held. This experiment was repeated sev-
eral times with identical results. Under these condi-
tions there seems to be little doubt but that the
QE37
100-
O ISOLATED
Q PAIRS
• GROUPS OF FOUR
€ GROUPS OF EIGHT
TRIAL 5 10 14
Fig. 32. Goldfish learn to swim a simple aquarium-
maze the more readily the more fish there are present.
(From Welty.)
i62
THE SOCIAL LIFE OF ANIMALS
groups of goldfish learned to move forward and se-
cure food more rapidly than the same number of
isolated fish.
The conditions of the experiments allow certain
TRIAL
Fig. 33. Isolated goldfish learn the problem set for
them less rapidly, and unlearn it more readily. (From
Welty.)
types of analyses to be made. One of these is to test
the tenacity with which the newly acquired habit
will be retained. A set of fish was trained as usual
(Figure 33). After ten days, when the grouped fish
had been letter-perfect for four days, although the
isolated goldfish were still taking some three min-
utes per trial, the experiment was changed; when-
GROUP BEHAVIOR 163
ever the fish came forward through the gate they
were offered pieces of worm soaked in acetic acid.
The isolated fish, perhaps because they had not
learned to perform so well, perhaps because they
were isolated or for some other reason, ceased to
react rapidly, and on the twenty-ninth day they were
averaging fifteen minutes per trial. The grouped
fish were much more steady in behavior, and per-
sisted in coming forward with relatively little change
until the twenty-seventh day; and even then the old
conditioning held for most of the fish most of the
time. Many individuals persisted in coming forward
through the gate for a long time after they ceased
biting or even swimming toward the acid-treated
worm.
When a group of fish are reacting together, if a
given individual moves forward through the gate to
the feeding space, others may follow because of a
group cohesion. It is obvious that if a fish is isolated
and moves forward, the faster reaction cannot affect
the behavior of other isolated fish.
With this in mind. Dr. Welty undertook a series
of experiments in which there were two partitions
in the aquarium, with one door opening forward
and another door opening through the other parti-
tion toward the rear of the aquarium (Figure 34).
164 THE SOCIAL LIFE OF ANIMALS
The fish were placed in the central space and those
in half the tanks were trained to come forward as
usual. In the other half, two selected fish were con-
ditioned to come forward and two were similarly
A ^
V
Fig. 34. The aquarium-maze used in training part of
the fish to come forward and part to go to the rear to
be fed. (From Welty.)
trained to move to the rear compartment to be fed.
The experiment was tried several times with gold-
fish, the minnow, Fundulus, common at Woods Hole,
and another marine minnow, Cyprinodon. For one
reason or another, only one series in which the fish
were comparable was successfully completed. The re-
sults are shown in Figure 35. Generally speaking,
the cohering groups of Cyprinodon learned more
rapidly and reacted more steadily than the separat-
ing groups. This, then, is one factor that is working,
GROUP BEHAVIOR 165
at least at times, in causing grouped fish to learn
more rapidly in a simple aquarium-maze than iso-
lated fishes under similar treatment.
As the goldfish move forward in the usual divided
ojo.i'
e SEW\RATinG GROUPS
O COHERIMQ GROUPS
TR»AL 5 10 J5 19
Fig. 35. Cyprinodon learn to move in a body more
readily than to split into two separate groups. (From
Welty.)
aquarium there comes a time when one or more fish
may be in front of the screen, and the others in the
rear of this advance guard. It was obviously a part
of the investigation to find the effect these more
rapidly reacting fish had upon their fellows merely
as a result of being in the forward chamber. Con-
ceivably they may have served as a lure. Another pos-
i66
THE SOCIAL LIFE OF ANIMALS
sibility is that a rapidly learning individual becomes
a leader in the reaction of the whole group.
Both of these possibilities were tested experi-
Qli5*
70
• 9
^ OCOMTROL
60
\ ©PLUS LURE
\ • PLUS LEADER
50
• #1
40
■ u
30
■ n
20
■ \l
to
f^io
D
C
- \_
OCOMTROL
©PLUS LURE
• PLUS LEADER
TRIAL
4 5
A
Fig. 36. Goldfish learn more readily if accompanied
by a trained leader than if there is a fish in the proper
position to act as lure. (From Welty.)
mentally by Dr. Welty, with results which are sum-
marized in Figure 36. Three sets of aquaria were
established. In the control aquaria all the goldfish,
of which there were four in each tank, were fish
which had had no previous experience in these ex-
periments. These were trained as usual. In another
set, an untrained fish was kept in each forward com-
GROUP BEHAVIOR 167
partment as a lure and four untrained fish were
placed in the rear compartment. These fish were
trained as usual; the so-called lure-fish was fed after
the first of the untrained lot came through the gate-
way. In the final set of aquaria a trained fish was in-
troduced along with the four untrained fish. When
the light was admitted and the gate was raised this
trained fish moved forward, came through the gate-
way, and was fed immediately. The others followed.
As the graphs show, after the first day there was lit-
tle difference in the reactions given by the control
fish and by those which had a lure-fish in front of
the screen. The fish with a trained leader generally
gave more rapid reactions than either of the others.
There is always a temptation to make comparisons
between the learning behavior of these laboratory
animals and that of men. Direct comparisons should
usually be avoided. However, in human terms, the
goldfish reacted more rapidly in the presence of a
trained leader which went through the whole be-
havior process with them, than they did to the pres-
ence of one of their kind as a lure-fish in the forward
compartment, a sort of signpost to proper behavior.
Evidently leaders working with these goldfish can in-
fluence them more than fish which by their posi-
tion merely show them where they can come. It
seems fair to say that with these fish demonstration
i68
THE SOCIAL LIFE OF ANIMALS
teaching is the most effective method yet discovered.
Still another attempt was made to study group
cohesion in these goldfish. For this purpose aquaria
Fig. 37. An aquarium-maze arranged to test the
power of observation of fish placed in the side compart-
ment. (From Welty.)
were arranged like those in Figure 37. At the side
of the usual aquarium-maze a narrow runway was
placed into which untrained goldfish were intro-
duced. In half of the tanks the glass partition was
clear and allowed the fish to see the reaction of those
GROUP BEHAVIOR
169
in the larger aquarium-maze. In the other half, the
partition was of opaque glass, cutting off the view.
O CLEAR GLASS
0 OPAQUE GLASS
t 2
TRIAL
Fig. 38. Goldfish react more rapidly if allowed to watch
others perform. (From Welty.)
Trained fish were placed in the aquarium-maze
and were run through their performance from ten
to twenty times in different experiments. The same
170 THE SOCIAL LIFE OF ANIMALS
treatment was given the fish in the aquaria with
opaque partitions and those with clear glass. The
trained fish were then removed and those from the
small side chamber were gently transferred to the
larger side. An hour later they were given an ordi-
nary test such as had been given to the trained fish.
As is clearly shown by the graphs in Figure 38, the
fish which had been able to watch the others react
behaved decidedly more like trained fish than those
which had not been able to see their fellows perform.
As a final check, the whole test was repeated, ex-
cept that no fish were placed in the larger side of
the aquarium. Fifteen times each aquarium was
lighted up, the door opened, and the experimenter
stood ready to feed any imaginary fish that might
come through. Then when those in the side passages
were transferred, there was no essential difference in
the behavior of the fish from the two types of
aquaria, and the experimenter was free from any sug-
gestion that he might have been signaling the fish.
The results of these experiments suggest that there
is such a thing as imitation among goldfish. Whether
there is or not depends, as Dr. Welty rightly says,
largely upon the definition given to the word imita-
tion. These fish probably do imitate each other on
a relatively simple instinctive level. The untrained
fish that watched the reaction of their trained fel-
GROUP BEHAVIOR 171
lows through the clear glass became conditioned in
two ways which were not open to the fish behind
an opaque glass. In the first place they saw the fish
move forward on the reception of a given stimulus,
pass through the gate, receive food, and give no evi-
dence of an avoiding or "fright" reaction. This prob-
ably gave what might be called a certain reassurance.
Secondly, they showed group cohesion, and moved
forward with the reacting fishes; at times they were
even seen to move forward in advance of the fishes
on the maze side of the aquarium.
When transferred to the aquarium-maze and given
the releasing stimulus of an increase in light, accom-
panied by the opening of the gate, both types of
previous experience probably played a role in pro-
ducing a faster reaction. Fish behind the opaque
glass could have neither of these helpful experi-
ences. When their narrow aquarium was flooded
with light they ordinarily moved back to the far end
and remained there. There was nothing to train
them to overcome this normally negative reaction.
So reviewed, it must be said that this behavior has
some points of resemblance to what is called imita-
tion in other animals.
There is also an element of imitation in the
greater food consumption of grouped fishes. One fish
sees another pursue, attack and consume a bit of
lyS THE SOCIAL LIFE OF ANIMALS
food and its own feeding mechanism is set off as a
result of this visual experience, even though its own
hunger might not have been sufficient to stimulate
feeding behavior. It is difficult to say to what ex-
tent such behavior is an expression of competition
as contrasted with unconscious co-operation. The
two types of motivation overlap here and elsewhere.
The evidence which we have been considering
furthers our understanding of the fundamental na-
ture of group activities among many animals, some
of which are not usually regarded as being truly so-
cial. The whole emphasis of this chapter has been
laid upon facilitation as the result of greater num-
bers being present. This kind of social facilitation
has been described for such diverse processes as breed-
ing behavior, eating, working and learning.
Added numbers do not always facilitate these ac-
tivities, as was shown by the analyses of the effect
of numbers upon the rate of learning. With some
animals, for example men and goldfish, under cer-
tain situations, learning is more rapid with several
present; but with others, such as parrakeets and mud-
minnows, under the conditions tested, increased num-
bers lead to a lower rate of learning. It seems that
no all-inclusive positive statement can as yet be made
in this field. One can, however, make the affirmation
that in the general realm here considered the pres-
GROUP BEHAVIOR 173
ence of additional numbers by no means always re-
tards, and is frequently stimulating. As before with
regard to other processes, we find that in certain
cases there are ill effects of undercrowding as well
as ill effects of overcrowding. Without careful ex-
perimental exploration, we cannot predict which
effect will emerge from a given situation.
One other result comes from these studies which
will help us to clarify evidence still to be presented,
as well as to review that already given. We have
come upon another measure of the existence of so-
cial behavior. Reactions may be regarded as social
in nature to the extent that they differ from those
that would be given if the animals w^ere alone. Such
differences are frequently quantitative, as they have
been in the cases we have discussed, although quali-
tative differences occur as a result of a change in
the numbers present.
From this point of view social behavior may have
or may lack positive survival value. All that is nec-
essary is that the behavior be different from that
which would be given if the animal were solitary.
In this sense all the animals whose behavior we have
been discussing are social to a considerable degree;
the more so, the greater the difference between their
behavior when grouped and when isolated.
When the behavior of such animals as cockroaches,
174 THE SOCIAL LIFE OF ANIMALS
fishes, birds and rats shows evidence of distinct modi-
fication as a result of more than one being present,
we have another suggestion that there exists a
broad substratum of partially social behavior. There
are many indications that this extends through the
whole animal kingdom. From such a substratum,
given suitable conditions, societies emerge now and
again as they have among ants and men. At these
higher social levels, as is to be expected, the type
of behavior shown under many conditions is related
even more closely to the number of animals present
than with less social cockroaches and fish.
VI.
Group Organization
WE ALL know that human society is more or less
closely organized. Sometimes, as in military circles,
some business organizations, and certain universities,
there is a line organization which extends in a defi-
nite order, step by step from the highest official to
the lowest rank. Frequently, however, the organiza-
tion is more complex, intricate and temporary.
We have known for some time, too, that in herds
of the larger mammals, where one can distinguish
different individuals, the group may be organized to
some extent with a dominant leader and frequently
with sub-leaders that stand out above the common
run of the herd. (16)
Despite this knowledge we have found with sur-
prise that other animal groups, a flock of birds for
example, in which the different birds are indistin-
guishable to the human eye, also are organized into
a social hierarchy, frequently with a well-recognized
social order which runs through the entire flock.
The situation that has been revealed in these flocks
175
176 THE SOCIAL LIFE OF ANIMALS
of birds is amusing, interesting and important
enough to warrant more attention than it is receiv-
ing at present.
Studies of the sort I am going to describe were
initiated by a Norwegian named Schjelderup-
Ebbe. (108) They were made possible by the use
of colored leg bands and other markings by which
the different individuals could be recognized by a
human observer. Apparently the birds themselves
knew the individual members of the flock without
such artificial aids.
Not because it is the most important work on the
subject, but because I can best vouch for it in de-
tail and in general, I shall present certain analyses
of group organizations that have been made in our
own laboratory.
The organization of flocks of chickens is fairly
firmly fixed. This is particularly the case with hens.
The social order is indicated by the giving and re-
ceiving of pecks, or by reaction to threats of peck-
ing; and hence the social hierarchy among birds is
frequently referred to as the peck-order.
When two chickens meet for the first time there
is either a fight or one gives way without fighting.
If one of the two is immature while the other is
fully developed, the older bird usually dominates.
Thereafter when these two meet the one which has
GROUP ORGANIZATION 177
acquired the peck-right, that is, the right to peck
another without being pecked in return, exercises it
except in the event of a successful revolt which, with
chickens, rarely occurs.
The intensity of pair contact-reactions varies
greatly. A superior may peck a subordinate severely,
or lightly, or it may only threaten to do so. It usually
turns its head, points its bill toward the subordinate
and takes a few steps in that direction. It may then
give a low deep characteristic sound which fre-
quently accompanies an actual peck, and stretch its
neck up and out without the resulting peck which
it seems just ready to administer.
The peck, when actually delivered, may be light,
heavy, or slashing. These vigorous pecks may be
painful even to man, as anyone can testify who has
tried to take a setting hen off her nest; and particu-
larly painful if repeated in the same spot. The peck-
ing bird may draw blood from the comb or may
pull feathers from the neck of the pecked fowl. The
peck is frequently aimed at the comb or the top of
the head; often it is not received with full force, for
the pecked bird dodges. Less often the peck is di-
rected toward back or shoulders.
The severity of a peck which lands as aimed is
illustrated by a recent observation in one of our
small flocks. One bird received a vicious peck di-
178
THE SOCIAL LIFE OF ANIMALS
rectly on the top of its head; it walked backward
two or three feet, staggered and fell, arose and again
walked backward in a blind course that took it into
the bird that had given the original peck. By that
RW pecks
all 12
A, BG, BB, M, Y, YY, BG^,
GR,
R,
GY, RY, RR.
RR pecks
11
A, BG, BB, M, Y, YY, BG^,
GR,
R,
GY, RY.
RY pecks
10
A, BG, BB, M, Y, YY, BG2,
GR,
R,
GY.
GY pecks
9
A, BG, BB, M, Y, YY, BG^,
GR,
R,
R pecks
8
A, BG, BB, M, Y, YY, BG^,
GR,
GR pecks
7
A, BG, BB, M, Y, YY, BG2.
BG2 pecks
6
A, BG, BB, M, Y, YY.
YY pecks
4
A, BG, BB, M.
M pecks
4
A, BG, BB, Y.
Y pecks
4
A, BG, BB, YY.
BB pecks
2
A, BG.
BG pecks
1
A.
A pecks
0
Fig. 39. Flocks of hens are organized into a definite
social hierarchy.
time the aggressor had turned to eating and paid no
attention to this chance contact.
As a result of patient watching of pecks received
and delivered, it is possible to find, with a high de-
gree of accuracy, the social status of birds in a rela-
tively small flock. (80) The organization of one such
flock of brown leghorn pullets is shown in Figure 39.
This peck-order was determined after sixty days of
observation. As shown by the chart, there was a
regular line organization down to the eighth bird.
GROUP ORGANIZATION 179
Then a triangle was encountered in which M pecked
Y, Y pecked YY and YY pecked M; and each of these
had the peck-right over the remaining members of
the flock.
Such irregularities are by no means uncommon
even in well-established flocks. A hen which is
otherwise the alpha bird in the pen may be pecked
with impunity by some low-ranking member, al-
though the latter is in turn pecked by many birds
over which the alpha hen has a clearly established
social superiority. This inconsistency may result
from the low-ranking bird having first met the
alpha bird on one of its off days, gained the advan-
tage in the first combat and managed to keep it
thereafter with the aid of the psychological domi-
nance thus established.
Similar social hierarchies exist also among flocks
of male birds. One flock of cockerels, which we
studied for seventy days, demonstrated the social
order shown in Figure 40 in which there are six
triangle situations that run through all the upper
part of the social scale, but are especially evident in
the middle ranks where B is involved in four of
them.
Cockerels are more pugnacious than pullets, even
when they are kept, as these were, on a diet which
somewhat restricts the tendency to fight. There were
l8o THE SOCIAL LIFE OF ANIMALS
more revolts and these were more likely to be suc-
cessful. For example, in this flock of cockerels, the
four birds lettered in bold-faced type in Figure 40
showed reversals, and with some the social rank had
BW pecks 9: W, BY, G, RY, B, BG, Y, R, GY.
BR pecks 8: W, BY, G, RY, BG, Y, R BW.
GY pecks 8: W, BY, G, RY, B, BG, Y, * BR.
R pecks 7: W, BY, G, RY, B, BG, GY.
Y pecks 6: W, BY, G, RY, BG, R.
GB pecks 5: W, BY, G, RY, B.
B pecks 4: W, G, RY, Y.
RY pecks 3: W, BY, G.
G pecks 2: W, BY.
BY pecks 2: W, B.
W pecks o.
In this order there are six triangle situations as follows:
GY R R GB B G
/ \ /\ A /\ A /\
B^^ BR Y-e— GY Y-^ B Y^h- B BY^RV B-^BY
Fig. 40. Cockerels also have a social organization which
is, however, somewhat more confused than with hens.
not been finally determined even after seventy days
of observations. Thus BY was observed to peck G
on six occasions, while G pecked BY eight times.
Ideally, in work of this kind, the birds should be
kept under observation throughout their waking
hours in order that we may have the full history of
their behavior. Such prolonged watching is imprac-
ticable, particularly since during much of the day
there is little pecking. Actually, observations were
GROUP ORGANIZATION l8l
restricted to the time near feeding, when the birds
were most likely to fight. Taken together with the
greater number of triangles, the reversals indicate a
less stable social order among these male birds than
among their sisters.
For a time there was no completely dominant bird
among the cockerels. BW, which stood highest in
general, was pecked by BR, which ranked otherwise
just below him. One day BR and Y started to fight,
as they had done many times before, with BR win-
ning. This time Y struck through to the eye, which
closed as a result, and BR retreated. The injury was
such that the tender-hearted observer thought that
BR needed special treatment, and removed him to
a hospital pen. The eye healed, and two weeks later
the recovered bird was returned to the flock which
he had almost dominated. In these two weeks of
absence he had lost his social status entirely, and
was pecked even by W, which had not been seen
before to peck a fellow cockerel. The reason for his
loss of position is not clear. He had been severely
injured, he had lost a fight to an inferior, and he
had been absent from the flock for fourteen days.
For one or all of these reasons he had lost caste so
completely that five days later he had to be removed
from the flock, literally to save his life.
During the five days that BR was again with the
l82 THE SOCIAL LIFE OF ANIMALS
flock, he avoided contacts with others as much as
possible, and spent a great deal of his time crowding
under a low shelf on which the water dish was kept.
In our experience, the lowest ranking chicken in a
flock tends to avoid social contacts as BR did after
his fall from superior position. Frequently the low-
ranking birds show many objective signs of fear.
They spend time in out-of-the-way places, feed after
others have fed, and make their way around cau-
tiously, apparently with an eye out to avoid con-
tacts. The lowest ranking birds may appear lean, and
their plumage is somewhat more rumpled because
they have less time to arrange it. Dominant birds,
on the other hand, are characterized by a complete
absence of signs of fear or of any attempt to avoid
birds of lower ranks. Some birds, usually those high
in the peck-order but not at the top of it, show few
avoiding reactions to their superiors, and, when
pecked, apparently take it lightly and pass on.
Chickens show some other interesting reactions
which are related to their position in the social
hierarchy to which they belong. Professor Murchi-
son, a psychologist at Clark University, has reported
studies on the behavior of a flock of six cocks and
five pullets. (83) In one series of experiments pair
after pair of the cocks were selected at random and
placed at either end of a narrow runway behind
GROUP ORGANIZATION 183
glass doors which allowed them full sight of each
other. When the glass doors were opened the cocks
ran toward each other. The point of meeting was
proportional to the relative position of the two in
the social scale, for the more dominant bird traveled
farther than the subordinate one.
In another experiment two cocks were placed in
small wire cages in which they were plainly visible,
and these cages were set in an enclosure about six
feet apart. If a third male from the flock were intro-
duced into the pen the free bird would go toward
the caged cock which was relatively lower in the
social scale. In this it behaved exactly opposite to
the females which were members of the same flock
and "acquainted" with both roosters. A hen released
under similar conditions is said to make her way
toward the cock that has the higher social position.
In our studies we have usually found that the
birds higher in the social order had more social
contacts than those that were at the bottom of the
peck-order. The correlation is not always exact, but
to date we have found few exceptions to the rule
that the bird lowest in the peck-order has the fewest
contacts. A quantitative difference, closely associated
with social rank, may be found in the number of
pecks delivered when there is no difference in the
total contacts among the upper birds. In a recent
184 THE SOCIAL LIFE OF ANIMALS
Study (9) in which four pens were under observation
with five or six pullets in each, out of 4,400 pecks
the ranking birds gave 1,800, the second in the lists
gave 1,092, and so on in regularly declining num-
bers until those next to the bottom gave 136 and
the birds that were lowest in their respective flocks
gave none at all.
Murchison has reported a variation of this general
rule. In studying the sexual behavior of his birds,
of the three cocks that gave the mating reaction the
number of treadings stood in direct relation to social
position, with the ranking cock treading pullets
most frequently. Interestingly enough, the top pullet
was also the bird which mated most frequently, and
the number of matings of the remaining females
was in direct proportion to their social position.
This appears to be a special case of the general rule
that birds high in the peck-order have more social
contacts than those that are low in social rank.
These are some of the known relationships exist-
ing among birds that have a relatively fixed group
organization. Schjelderup-Ebbe, (109, 110) who has
made observations on over fifty species of birds, in-
cluding, besides the common chicken, a sparrow,
various ducks, geese, pheasants, cockatoos, parrots,
and the common caged canary, is convinced that des-
potism is one of the major biological principles;
GROUP ORGANIZATION 1 85
that whenever two birds are together invariably one
is despot and the other subservient and both know
it. He has said, "Despotism is the basic idea of the
world, indissolubly bound up with all life and exist-
ence. On it rests the meaning of the struggle for
existence." He applies this principle to interactions
of men and of other animals and even to lifeless
things. He says: "There is nothing that does not
have a despot . . . usually a great number of des-
pots. The storm is despot over the water; the light-
ning over the rock; water over the stone which it
dissolves"; and he cites with approval the old Ger-
man proverb that God is despot over the Devil.
This poetry of Schjelderup-Ebbe's is striking, but
does it rightly interpret the facts? We have spent a
considerable amount of time at Chicago, investi-
gating the social order of various birds. Messrs.
Masure, Shoemaker, Collias and Kellogg and Miss
Bennett have been particularly active iii this work.
We have not yet studied as many varieties of birds
as Schjelderup-Ebbe, and we have no experience to
report about the relation between God and the
Devil. Of the birds we have studied, only the flocks
of white-throated sparrows approach the common
chickens in the fixity of their social hierarchies, and
they do not equal it. The common pigeon, the ring
dove, the common canary and parrakeets show a less
l86 THE SOCIAL LIFE OF ANIMALS
rigid type of social organization which I can illus-
trate by explaining the situation as we have found
it among common pigeons. (80)
The observations were made on a group of four-
teen white king pigeons, half of which were male
and half female. Their social order was observed in
sex-segregated flocks until, after a month, it seemed
to be fairly stable; then the flocks were combined,
and after a month during which five of the seven
possible pairs mated, the sexes were again segregated
for twenty-eight days of further study. The results
are essentially similar both for the males and the
females for the period when the sexes were separate,
so that I shall follow only the reactions of the fe-
male flock. The essential facts can be described with
the aid of the diagrams in Figure 41. These show
the social interactions between the females lowest in
the social order.
Let us examine Chart A with some care. This
charts the relationships of the five birds that were
lowest in the pre-mating flock. All these were domi-
nated in the main by BY and BB. The figures show
that BR was seen to peck GW ten times and was
pecked by GW, and retreated from her nine times.
GW pecked BW thirteen times, but lost in four
encounters. BR won ten and lost seven of its ob-
served contacts with BW, which won thirteen and
GROUP ORGANIZATION
187
lost ten with RY. RY in turn was practically even
(eight to seven) with BR and slightly ahead in its
relations with GW and RW. I do not intend to sug-
GW
12:27
mv
GW
>BW
8:14
RfV
^BW
RY<r
■BIV
13 UO
A.
Fig. 41. In flocks of pigeons the organization is one
of peck-dominance rather than of peck-right. The
pigeons highest in the social order are omitted from
these diagrams. A, the pre-mating flock; B, the entire
period of observation; C, the post-mating flock.
gest that most of these differences are important; in
fact that is the point. With flocks which are organ-
ized as are these pigeons, it frequently becomes diffi-
cult to decide which bird stands higher in the social
order.
It is important to note that in none of these cases,
l88 THE SOCIAL LIFE OF ANIMALS
in fact in only one of all the different reaction pairs
whose behavior is summarized in these charts, was
there an absolute dominance of one bird by the
other, and then only two contact reactions were
seen. When all contacts throughout the whole period
of observation are considered, there was at least one
time for each of the contact pairs when the bird
which usually lost out dominated the contact reac-
tion.
In Chart B, which shows all the reactions during
pre- and post-mating, and in C which records the
contacts for the post-mating season only, the four
birds represented by the diagrams were dominated
by three others, RY, BY and BB. It is worth empha-
sizing that with these birds an absolute despotism
was not established. Even RY, which more than any
other bird dominated the post-mating flock, lost con-
tact reactions to each of the others except to RW,
which was lowest of all. While it was winning 329
reactions it lost 58, and each of the other females,
RW excepted, dominated it at least three times in
the post-mating observations.
The picture that emerges is one of a flock which
is organized into a social hierarchy, but one which
is not so hard and fast as that found with chickens.
In the long run one becomes fairly sure which bird
in each of the groups will dominate in the larger
GROUP ORGANIZATION 189
number of their contacts, but the result of the next
meeting between two individuals is not to be known
with certainty until it has taken place. Within the
same hour and even within a few minutes reversals
in dominance may take place without anything un-
usual in the circumstances.
Putting the matter somewhat facetiously, chickens
appear to have developed the sort of "line organiza-
tion" characteristic of a military system or a fascist
state, while these pigeons, together with the ring
doves, canaries and parrakeets, are more democratic.
The social hierarchy among chickens is based on
an almost absolute peck-right which smacks strongly
of the despotism of which Schjelderup-Ebbe writes,
while these other birds have an organization based
on peck-dominance rather than on absolute peck-
right.
With such birds social position is not fixed once
and for all. Consider the case of RY among pigeons.
When results were first thrown together at the end
of two weeks of observation, RY was at the bottom
of the flock, a position which it retained for twelve
more days. Then something began to happen. What
it was, I wish I knew. RY began to go up in her
social world. After six days she. ranked a shaky third,
clearly dominated on the average by BY and BB.
Then the pigeons were allowed to mate. During
igO THE SOCIAL LIFE OF ANIMALS
the mating period BY, which was top bird in the
pre-mating flock of females, and RY did not pair off
with any of the males. Again I do not know why.
After the experiment was finished RY was carefully
autopsied and we could find no evidence of any-
thing physically abnormal. When the sexes were
again segregated RY was the top-ranking bird among
her fellow females, and remained so. She was seen
to have loi contacts with BY, the former alpha bird,
and to win 83 of them; she had 77 observed contacts
with BB, which had formerly been second from the
top, and defeated her 53 times. In the pre-mating
period RY lost two combats for each that she won;
in the post-mating flock she won five contacts for
each that was lost.
This raises in a rather dramatic fashion questions
as to what qualities make for a dominant bird. This
problem is not yet solved. With these birds, social
rank is in part a matter of seniority. Mature chickens
usually dominate immature ones and maintain their
dominance long after the former youngsters have
become fully mature and possibly physically able to
displace the senior members. This is good evidence
that memory of former defeats plays a role in main-
taining the social order once it is established. When
chickens strange to each other are put together for
the first time dominance usually goes to the bird
GROUP ORGANIZATION I91
with superior fighting or bluffing ability. Maturity,
strength, courage, pugnacity and health, all seem
essential qualities making for dominance among
chickens. Luck of combat also seems to play a part
when one considers the numerous triangle situations
that have been discovered. Since cockerels have cer-
tain of these qualities more than pullets, a male
bird, if present, dominates a flock of hens.
There seems to be little if any correlation between
greater weight and position in the peck-order. The
location of the combat seems to be important.
Schjelderup-Ebbe found that chickens in their home
yard win more combats than strangers to that yard;
and Mr. Shoemaker has reported that, with canaries,
each bird becomes dominant in the region near its
nest. (113) We found some years ago that with
pigeons one might be dominant on the ground
about the feed pan and another have first rank at
the entrance to the roosts. (80)
With chickens, as I have said, the larger, stronger,
more pugnacious males usually dominate the fe-
males. This is said to be generally true in species
in which the male is larger or more showy than the
female. With the parrakeets, (11) whose social order
in many ways resembles that of pigeons, the females
are dominant over the males except in the breeding
season. While breeding and nesting are in progress
192 THE SOCIAL LIFE OF ANIMALS
positions are reversed, and a previously hen-pecked
male may drive his usually dominant mate back
onto the nest when she attempts to leave it. The
sexes in these parrakeets can be told apart only by
slight differences in color.
When hens are giving the brooding reaction or
are caring for small chickens, they become less sub-
missive to other hens. Some of the other birds, whose
social ranking has been investigated, move up and
down in the social scale according to the phase of
the breeding and nesting cycle which they are in at
the time.
It has been reported that with hens those high in
the peck-order have a higher IQ than their more
lowly placed flock mates. (72) The IQ was measured
in this case by placing grains of corn out on the
floor with every other grain securely fastened down,
and finding the speed and accuracy with which the
fowls would learn to peck at the loose grains only.
We have had as yet only the most casual personal
contact with this problem so far as chickens are con-
cerned. With the parrakeets, Masure and I could
find no evidence of a positive correlation between
any aspect of ability to learn a maze and social rank.
From this summary it is evident that in spite of
a great deal of study we do not know all the factors
which determine the position of birds in their social
GROUP ORGANIZATION 193
order. There is some suggestion from the effect of
broodiness in hens and from observations on the
nesting cycle in canaries that there may be elements
of control by hormones. This lead is being investi-
gated actively at present, but I have no definite re-
sults to report. (6)
Some of the complications in determining the fac-
tors that make for dominance are shown by the pre-
liminary summary which Mr. Shoemaker has given
me of his studies on the social hierarchy in canaries.
The space available for the caged flock is a matter
of importance. When confined in relatively small
space, the social order becomes more simple and
definite and there is no complication over the ques-
tion of territorial rights. With more space, as for
example in a large flight cage, individual territories
tend to become established in which the particular
bird is supreme even though it ranks low in the
neutral ground around the bath bowls, the feeding
places, or regions where nesting material is stored.
When canaries are allowed to mate and small
nesting cages are supplied around the walls of the
flight cage, each individual male is master in its own
nest cage and controls more or less territory around
the cage entrance. Under these conditions even the
birds lowest in the social order dominate in some
restricted space about their nest.
194 THE SOCIAL LIFE OF ANIMALS
In general these canaries show more pecking
among the males than among the females, and dur-
ing the nesting period the female does little to de-
fend the nest territory; that is the work of her mate.
In this home territory the social dominance of the
male over his fellow males is not steady but varies
with different phases of the breeding cycle. During
the processes of nest-building, egg-laying and incu-
bation, the male tends to become more dominant.
This is shown by an increase in the size of the ter-
ritory about the nest which he dominates, and by
the fact that when on neutral territory he tends to
win more of his pair contacts. During the rest of
the cycle the male tends to lose dominance as meas-
ured by both these criteria.
It is worth noting that in the course of these pul-
sations in dominance the male may not actually
move up in the social scale as determined by the
number of birds which he fully dominates. He may
win more of his individual pair contacts without
actually oversetting the usual trend. The same bird
may show fluctuations in dominance during the day.
Thus one male regularly dominated less territory of
an evening than he did in the morning. This may
well be a matter of stamina.
In some cases the relation between the sexes in
these canaries hinges on another complication. For
GROUP ORGANIZATION I95
example, a female, 15, mated with a male, 55, which
stood about midway in the social order among the
males: 55 dominated the other females and all the
other males dominated over 15. However, of thirty-
three observed contacts between 15 and 55, the male
lost all but one! The male parrakeet will drive back
on her nest the female who has left it, but 55, like
other male canaries, coaxed his mate back to her nest
with offers of food.
Until studies are further advanced, we cannot be
sure how many of these complications which Mr.
Shoemaker has recorded for the canaries are found
elsewhere even among birds. It seems reasonable to
suppose, however, that the social hierarchy is rarely
as simple in its organization as a mere listing of the
social ranking seems to indicate.
With all these birds, high rank in the social order
of the flock means much greater freedom of action,
more ready access to food and a generally less
strained style of living. It is hard to say whether in
nature it means more than this, although it seems
probable that in times of food shortage, or other
phases of environmental stress, the ranking birds
who have the first opportunity at food might readily
fare better than those low in t,he social scale. Fortu-
nately, enough observations have been made in na-
ture so we know that with some species the peck-
196 THE SOCIAL LIFE OF ANIMALS
order, which has been most studied in restricted
cages and pens, does occur in the wild.
The alpha bird in a penned flock of chickens does
not necessarily lead in foraging expeditions when
the flock has more space. Fischel, a German, reports
that when hens of known peck-order are released
to forage in an orchard the dominant and near-
dominant birds may or may not be at the apex of
the foraging flock. (46) Usually the leadership
changes from time to time and moreover the lead-
ing bird seems always more or less dependent upon
her followers. If she gets too far out ahead the leader
turns back and rejoins the flock or waits for them
to catch up. Similar hesitation by the leader when
it has advanced some distance in front of its fol-
lowers has been observed among other animals, no-
tably among ants and men.
This problem of leadership among birds is related
to, but not identical with, position in the social
order. There are many aspects of the problem into
which we cannot go at present, pending a closer and
more revealing study than has appeared as yet of
the qualities that make for leadership.
With some herds or hordes of mammals leader-
ship rests with an old and experienced female. (16)
In such herds the females and young frequently
make up the more stable part of the social group.
GROUP ORGANIZATION 197
to which males attach themselves during the mating
season. With other mammals the male is the leader,
and sometimes a jealous one, that drives other males
out of the herd; although in some cases several males
are tolerated. (3)
Leadership does not always go to the faster or
stronger animal; in fact, the position of being out
in front of the flock may not mean real leadership.
An interesting example of such pseudo-leadership
has been recorded for a mixed group of shore birds
observed by Mr. Nichols of the American Museum
of Natural History. (85)
He found a mixed flock of such birds which was
composed of two young dowitchers, with a dozen
black-bellied plovers and a single golden plover.
Under these conditions certain of the birds could
readily be distinguished from the others. When the
flock was flushed, the flight of the golden plover was
comparatively rapid and it was soon ahead of all of
the rest. The dowitchers were slow and tended to
fall behind, and when this happened the black-
bellied plover wheeled. This affected both the ap-
parent leader, the golden plover, and the lagging
dowitchers. The former, finding itself alone with-
out followers, rose above the. flock, took the new
direction and dived down with a few swift wing
beats, again the apparent leader of them all. The
igS THE SOCIAL LIFE OF ANIMALS
slower dowitchers took the chord of the arc made
by the wheeling flock and so caught up with and
again became an integral part of the flying group.
Soon again the slow dowitchers lagged and the whole
performance was repeated.
These observations do not reveal the stimulus
which releases the wheeling mechanism of the main
flock. The simplest explanation, that the leader, find-
ing himself out alone in front, starts to turn and
so gives a stimulus to the keen-sighted remainder so
that they also shift direction almost instantaneously,
does not hold in this mixed flock, for the observa-
tions indicate clearly that the apparent leader, the
golden plover, was following along in front of the
main flock as much as the slow dowitchers were fol-
lowing along behind it.
Neither does this simple-leadership sort of ex-
planation fit the facts as observed among wheeling
flocks of other shore birds or of pigeons. In such
flocks the stimulus to turn frequently seems to
originate in one of the flanks, and spreads from that
point rapidly through the flock. Here again the ap-
parent leaders may not be the actual ones. It is pos-
sible, though we are not yet sure of it, that in such
flocks made of birds which we cannot tell apart, the
faster individuals also may dive through the flock
GROUP ORGANIZATION I99
to the foremost position, taking their direction from
the whole flock.
However the signal for turning, originates, the
wheeling takes place so rapidly that mythical ex-
planations are still being advanced. I have a small
book written on the subject by an English author,
called, Thought-transference (or What) in Birds?
(ill) The title correctly summarizes the contents of
the book.
I would not have you conclude from my repeated
emphasis on the absence of definite leadership in
these flocks of birds, and on the presence of a
pseudo-leadership when the flock is really determin-
ing the direction that is taken by the bird in front,
that there is no real leadership among other animals
and among men. And I must make it clear that here
I am speaking of real leadership and not of a peck-
order, which, as is true with social position in human
society, does not imply leadership at all. Such a po-
sition could not be successfully maintained by a per-
son trained in science rather than in dialectics. But
apparently, at least among so-called lower animals,
the leader is frequently as dependent on his fol-
lowers as they are on him, and sometimes even more
so. A similar situation occurs in human affairs often
enough and under such a variety of situations that
the relationship deserves more careful consideration
200 THE SOCIAL LIFE OF ANIMALS
than it usually receives when problems of leadership
are discussed.
While those of us who have been engaged in these
studies have probably never been wholly unaware
of the possibility of amusing cross-references to man,
I must insist that our motivation has not been that
of making an oblique attack upon human social re-
lations. Rather, we have found problems concerned
with the social organization of birds and other ani-
mals interesting and important on their own ac-
count.
We have, of course, a feeling that different ani-
mals have much in common in group psychology
and in sociology, as well as in more distinctly physio-
logical processes. It is the viewpoint of general
physiology that we cannot understand the working
and the possibilities of the human nervous system,
for example, without study of the functioning of
the nervous systems of many other kinds of animals.
Similarly well-integrated information has been com-
piled concerning general and comparative psychol-
ogy. From the same point of view some of us have
been trying to develop a general sociology, which
even in its present imperfect state allows human
social reactions to be viewed in part as the peculiar
human development of social tendencies which also
have their peculiar developments among insects.
GROUP ORGANIZATION 20I
birds, fish, mice, and monkeys; that is, among social
animals generally.
Keeping this point of view, and with our back-
ground of studies of social organization, it is worth
while to turn for a short consideration of the actual
application of similarly objective studies in certain
human groups. I pass over the possibilities of study-
ing the peck-order in women's clubs, faculty groups,
families or churches, to call your attention to some
studies that have recently been published dealing
with the social interactions of the Dionne quin-
tuplets, since these will serve to throw light on a
number of interesting points. (25)
In all questions of dominance in the group or of
other forms of social inequality, we come immedi-
ately and continually upon the question of the ex-
tent to which these observed social differences are a
matter of heredity and to what extent they follow
differences in training or other environmental im-
pacts. This is the old nature-nurture problem, other
aspects of which have been discussed for years.
Driven by many different kinds of evidence, biolo-
gists have come to the conclusion that all men are
not born equal. Applying this to social affairs we
have the general assumption that many of the ob-
served differences in social position are a result of
the inherited differences depending on the vagaries
202 THE SOCIAL LIFE OF ANIMALS
of bi-parental inheritance and more remotely on
mutations of one kind or another.
Fortunately we have in the case of the Dionne
quintuplets a natural experiment which deserves
much attention. Detailed biological studies which
appeared late in 1937 confirmed the general assump-
tion that these much-discussed babies are an iden-
tical set of sisters. Biologically this means that all
of them have come from one ovum which was fer-
tilized by one spermatozoan. Soon after fertilization
the early cleavage cells separated and produced five
embryos, each with identical heredity. I shall not
give the details of the evidence on which this con-
clusion is based. In addition to looking so much
alike that only their regular attendants can tell them
apart with any degree of sureness, there are simi-
larities in finger and palm prints, in toe and sole
prints, and in other anatomic details which point
conclusively toward a common identical heredity.
A group of investigators from the University of
Toronto have been studying the social reactions of
the quintuplets and have reported observations from
the twelfth to the thirty-sixth month of their age.
At first the children were placed together in a play
pen by pairs to observe their interactions; from the
twenty-second to the thirty-sixth month they were
observed as a group.
GROUP ORGANIZATION 203
The available records do not allow an exact com-
parison with the peck-order I have described for
various birds. The observers were interested in re-
cording and analyzing the following bits of behavior:
1. Total contact reactions.
2. Reactions of one child toward another, which
they call to reactions. A to reaction by one child
will be a jrom reaction for the child receiving the
attention.
3. Whether the reactions are initiated or are re-
sponse bits of behavior. An illustration will help to
make this clear. If A pushes Y, it is regarded as an
initiated to reaction by A, while Y is credited with
a from reaction. If Y pushes back, then this is a re-
sponse to reaction for Y and a from reaction for A.
4. They also record which child watched which
one.
I shall not use all these distinctions for my points
can be made accurately with only part of them.
As shown in Figure 42, certain reactions are
summarized in the top row for the entire period
from the twenty-second to the thirty-sixth month,
and in the lower row the same reactions for the last
four months of the study, from the thirty-second to
the thirty-sixth month. The left-hand diagrams give
the total contact reactions during these respective
periods. The center diagrams show the total to reac-
204 THE SOCIAL LIFE OF ANIMALS
tions and those on the right give the initiated to
reactions.
Let us examine the upper left figure. A had a
AGE: 22-36 MONTHS
740
375.
169
A
622
c
550
Y
421
Fi
A
301
c
264
Y
2?9
m
A
125
c
114
M
102
go
M
E
M
E
E
Y
2
3
1
5
4
2
3
1
5
4
2
3
5
4
,
<— MENTAL RAWK
100 84 74 58 54
TOTAL CONTACTS
346
515
a'
132
2 3 15 4
100 50 70 61 53
TOTAL TO CONTACTS
176
149
74 68 60 53 «— PER CENT
A
53
49
c
M
29
L27
Y
E
?.
3
5
1
4
♦—MENTAL RANK
100 90 62 52 40
100 85 61 56 37
AGE: 32-36 M0NTH5
67 62 37 34 <— P£R CENT
Fig. 42. The Dionne quintuplets also show evidence of
a social organization among themselves.
total of 740 observed contacts directed to and re-
ceived from her sisters. This is taken as lOO per cent.
C had similarly 622 contacts, which were 84 per
cent of A's, and so on, with Y third, M fourth, and
E fifth. The order in total number of contacts then
GROUP ORGANIZATION 205
is A, C, Y, M, E. This same order holds for total to
contacts and for both total and to contacts in the
thirty-two to thirty-six months' period. The diagrams
on the right show that A initiated the most to con-
tacts, and that C was next. Beyond that the order
varies. For the whole period of observation (upper
row) it is M, E, Y, and for the last period (lower
row) it stands as M, Y, E.
The other available data do not always give this
same order, but enough has been presented to show
that, among these children identical in heredity and
almost so in post-natal environment, there are social
differences which can be recognized by the behavior
of the children toward each other.
As the figures giving mental rank indicate, the
correlation with intelligence is by no means perfect.
Neither is the correlation with size. Y, the largest,
and said in some ways to be the most mature of the
five, ranks in the tests shown here from third to
fifth. And while M, the smallest, ranks low, she is
not the lowest, and other data show that in the per-
centage of her contacts which were self-initiated to
reactions she ranks first of all these sisters.
These observed differences raise an interesting
question: If heredity has been the same and the
environment constant, how did the differences creep
in? It is possible that there are unobserved, unrec-
206 THE SOCIAL LIFE OF ANIMALS
ognized differences either in the handling of the
children, in their early contacts with each other, or
in their impacts with their physical environment
which may have been cumulative enough to pro-
duce these social differences. It is also possible, as
Professor H. H. Newman suggests, that the differ-
ences are environmental after all. We must remem-
ber that from the standpoint of A, C, Y, M, and E,
their environmental relations began long before
birth, and though the care given them since birth
may have been practically identical in each case, it
may not have been possible to erase environmental
conditions impressed upon them during their seven
critical months of intra-uterine life.
Whatever the reason, we have come to an inter-
esting, and, I think, important conclusion, which is
that animals with exactly the same heredity may
still develop, even at an early age, graded social dif-
ferences showing that one is not exactly equal to
the other. We have indications that the same prin-
ciple holds among birds, but even if present indica-
tions are finally borne out, the experiment will not
be as elegant, in the strictly scientific sense, as are
these observations on the Dionne quintuplets.
Finally, by way of review, there exists among
flocks of birds, even though they may be identical
to the human eye, a graded series of reactions within
GROUP ORGANIZATION 207
the flock which allow observers to rank the birds in
the order of their social dominance. This social
order may be relatively hard and fast, as with hens,
or more loosely organized on a give-and-take basis
among pigeons and canaries. The factors under-
lying the social order in these birds are complicated
and include such personal traits as age, pugnacity,
sex in general and the reproductive cycle in par-
ticular, as well as such environmental factors as size
of available space and the possibilities of establish-
ing special territories. High position in the social
order does not necessarily coincide with group lead-
ership, although at times it does. The survival value
of high position in the social hierarchy has not been
demonstrated, but there are many reasons for sus-
pecting that it may be felt in times of famine or
during other periods of environmental stress.
The problems related to leadership, although
mentioned, were not discussed exhaustively. Em-
phasis was laid on the importance to the leader of
his followers, and on the existence of a pseudo-
leadership in which the animal in front is taking
direction from his apparent followers.
With the Dionne quintuplets it was demonstrated
that social differences exist even with children that
have identical heredity, and a theory of environ-
mental differences was favored as an explanation.
2o8 THE SOCIAL LIFE OF ANIMALS
In conclusion, the social organization observed in
birds and other animals reminds one almost con-
stantly of certain types of human social situations.
The dominance-subordination relations of people
are at times readily observed; at other times they
are obscured by other social responses. When present
in man, patterns of domination may be expressed in
many more ways than in birds or mice. It may well
be that the social hierarchies of chickens, canaries
and men have much in common. Without taking
the comparison too seriously, the fact that chickens,
for example, have a relatively simple system of des-
potism may help explain, though it does not justify,
the appearance of a similar social organization in
man. Other types of social organization also exist
among the other animals, and man need develop
only that best suited to his unique situation.
VII
Some Human Implications
WHILE WE have been engaged in trying to assay
the relative importance of the principle of co-opera-
tion among animals, we have given most of our time
and attention to its manifestation among animals
considered to be asocial or only partially social. In
such animals it is an unconscious kind of mutualism,
but its roots are deep and well established and its
expression grows to be so spontaneous and normal
that we are likely to overlook or forget it in the more
striking exhibition of social co-operation among
higher animals. Conscious co-operation is so com-
paratively new in an animal world many millions
of years old, that we may underrate its strength and
importance if we are not reminded of its foundations
in simple physiology and primitive instinct.
When we attempt to apply to human behavior the
same methods of analysis that we have used through-
out toward other animal groups, we reach most in-
teresting results when we select some phase of reac-
tions of men in which integration has not developed
209
210 THE SOCIAL LIFE OF ANIMALS
much beyond that found in some of the semi- or
quasi-social animal aggregations which we have been
considering in the lower animals.
Among the possible aspects of human behavior
that meet this requirement and that lend themselves
to biological analyses is the whole set of activities
that center about the relations between nations.
Even the most optimistic humanist will not main-
tain that these are at present, or ever have been, on
as high a social plane as that which characterizes
many of the personal interactions of mankind, or
those of the smaller social groupings of men.
The most casual reading of recent events is con-
vincing evidence that the modern international sys-
tem is based on war. This final resort to violence
has been regarded by many thoughtful people as in-
evitable, man being what he is, that is, the product
by natural selection of the results produced by the
struggle for existence; for the ordinary thoughtful
person is not aware that the tendency toward a strug-
gle for existence is balanced and opposed by the
strong influence of the co-operative urge. Because
of this common attitude toward war, and because
of its fundamental importance to our species, I pro-
pose to cut through the shifting tangle of interna-
tional policies down to the basic biological signifi-
cance which it holds for us.
HUMAN IMPLICATIONS 211
In doing so I must recognize these two funda-
mental principles, the struggle for existence and the
necessity for co-operation, both of which, consciously
or unconsciously, penetrate all nature; and I shall
say now that we may find that these two principles
are not always in direct opposition to each other;
that there is evidence that these basic forces have
acted together to shape the course of evolution, even
the evolution of social relations among men and na-
tions of men.
If, in the past, we have not had facts on which
to base rational conclusions about national problems,
it cannot be said that we have not had powerful
emotions to drive us into one attitude or the other.
It is very difficult to keep an objective, unemotional
attitude toward the complex subject of the biology
of war. We may not agree in our placing of the
emphasis, but I trust that when we disagree it will
be on a healthy intellectual level.
It is clear that we are entering a tricky field where,
to a greater extent than usual, the evidence is not
all in, and one in which much that we think we
know is contradictory. No one can bring this prob-
lem into the laboratory for careful testing. We must
do the best we can with inforraation which is more
incomplete and faulty than that on which we nor-
mally base our biological discussions. The human
212 THE SOCIAL LIFE OF ANIMALS
importance of the subject justifies the risk. The pres-
ent discussion will center about three main points:
1. To what extent do the underlying biological
relationships tend to bring about war?
2. Is war biologically justified by the results pro-
duced?
3. Can the basic principles of struggle and of co-
operation work together in the international rela-
tions of men?
Many men are aggressive animals. The similari-
ties between human social hierarchies and those of
chickens and other animals emphasize similarities of
the drive toward dominance in the species concerned.
Our immediate question is: Does this human aggres-
siveness mean that men have an inherent, instinctive
drive toward war? The ideal way to attack this prob-
lem would be to rear sizable groups of people free
from contact with outside influence or social tradi-
tion and see whether under these conditions they
would instinctively engage in group combats in order
to forward or defend group ambitions.
Such objective procedure is out of the question,
but an interesting subjective inquiry has been made.
In 1935, American psychologists took a poll among
themselves on the question as to whether they be-
lieved that the tendency toward making war is an
instinctive drive in man. Of those answering^, well
HUMAN IMPLICATIONS 213
over 90 per cent said that there is no proof that war
is an innate behavior pattern. (129) Less than 10 per
cent thought that war represents an instinctive re-
action. I did not personally see this questionnaire
but I am credibly informed that the question was
stated fairly and did not suggest the type of answer
expected.
This is a rather unexpected unanimity, and may
be accounted for to a minor degree by the existence
of one modern school of psychologists that doubt
the possibility of instinctive action, particularly
among men. I do not think they represent a large
proportion of American psychologists but there may
have been enough of them to have lifted the per-
centage high.
The opinion of the psychologists is supported by
the independent judgment of one of the leading
students of anthropology, Professor Malinow^ski, who
said in his Harvard tercentennial lecture: (78) "All
the wrangles as to the innate pacifism or aggressive-
ness of primitive man are based on the use of words
without definition. To label all brawling, squab-
bling, dealing of black eye or broken jaw, war^ as is
frequently done, simply leads to confusion. War can
be defined as the use of organized force between
two politically independent units, in the pursuit of
214 THE SOCIAL LIFE OF ANIMALS
tribal policy. War in this sense enters fairly late
into the development of human societies."
It is not impossible to break down and re-make in-
stinctive behavior, as the change in marriage cus-
toms since the days of the cave man shows us. Never-
theless, it is much easier to change learned behavior
patterns, one of which these experts believe war to
be.
We must still take account of individual aggres-
siveness, and the fact that man appears to be rela-
tively easy to lead into mass combat. Even if war-
making is not instinctive, if it is a learned pattern
of social behavior, there is evidence that it has
existed for some fifty centuries, and it would prob-
ably require at least a few centuries of intelligent
and fairly concerted effort by those who do not be-
lieve in its utility to unlearn the habit.
There is a second important set of biological proc-
esses which at first sight appear to work inevitably
toward the production of war. These center about
the question of overpopulation, that is to say, about
the relation human numbers bear to habitable land
areas. This is the next primary problem which we
must consider.
Over the world there is a limited range of habit-
able land; and thus far we have no intimation of
any practical method of emigration to neighboring
HUMAN IMPLICATIONS 8I5
and perhaps less occupied planets. And there is a
rapidly expanding human population, which is even
now becoming uncomfortably dense in the crowded
nations. It is often said that this is a fundamental
cause of tension which makes wars inevitable, as
hard-pressed dense populations seek food in more
amply-provided areas.
The desirable biological results of wars so induced
have been, and still are, supposed to be two:
1. The dense populations are thinned to the bear-
able point as a result of the fighting, or
2. Superior nations, or races, are victors. They
expand at the expense of the defeated inferior group
and so occupy more of the limited space which is
available for men.
Let us test these theories against the known facts.
Roughly speaking, there are about fifty-two million
square miles of land surface on the earth. (95) This
includes the habitable plains of the temperate re-
gions; it also includes the relatively uninhabited
deserts, tropical jungles, and mountains. Approxi-
mately one-fourth of these fifty-two million square
miles is desert or semi-desert and can support only
a sparse population of men. This leaves roughly
forty million square miles of non-arid land theoreti-
cally open to human habitation.
On this land there are living at present, accord-
210 THE SOCIAL LIFE OF ANIMALS
ing to a 1935 revision of the estimated world popula-
tion which was made by Professor Pearl, something
over two thousand millions of people. This is almost
exactly forty people per square mile of the whole
earth's surface, or about fifty people per square mile,
if the arid and semi-arid land is excluded. We can
better visualize the meaning of these figures when
we know that they are almost exactly the average
population density for the United States; forty per
square mile for the whole land area, and fifty per
square mile if on land with fair rainfall.
A recent estimate of human population of three
hundred years ago, tentatively advanced by Profes-
sor Pearl, is that in 1630 there were probably about
445 million people on the whole earth, or about
eight per square mile of total land surface. (95) Dr.
Pearl thinks that this was probably the largest hu-
man population which the earth had supported up
to that time. Then came the opening of the Americas
for settlement, and the beginnings of modern use
of transport and manufacturing processes, and the
scattering of information by modern methods. The
result has been that in the last three centuries the
population of the world has increased almost five-
fold, from eight to forty per square mile, largely
because food and shelter and mechanical energy were
made available for five times as many people, and
HUMAN IMPLICATIONS 217
because the development of modern science made
the world safer for them.
In these three hundred years the world popula-
tion has doubled, on the average, approximately
every sixty-four years. Today mankind is increasing
in numbers at such a rate that if the increase should
continue as it was going in 1935 we could expect
another doubling of the number of people in the
world in approximately seventy years, and we should
have about eighty people per square mile in the
year 2005.
What then? Will not the coming generations at
some time be obliged to fight for their place in the
sun?
This prospect is somewhat altered, however, by
the fact that many students of population trends
believe that the rate of human increase is slowing
down. In the case of the United States, Dr. Baker,
(20) economist of our Department of Agriculture,
has estimated recently that unless present trends are
changed (and they may be) there will be a further
population increase in the United States of only
about eight million in the next two decades. He
thinks that the population will then have reached
its maximum, if conditions remain as they are today.
Thus, according to Dr. Baker, we are looking for-
ward to a maximum population of less than 150
2l8 THE SOCIAL LIFE OF ANIMALS
million people, or less than fifty for every square
mile of our country. Others put the figure higher,
but I know of no expert who expects our Ameri-
can population to double itself again unless there is
a radical increase in available energy or in other
aspects of our living conditions.
For the world as a whole. Dr. Pearl estimated in
1936 that, if present trends continue, as they may
not, the world population will reach a maximum of
about 2,650 millions by the year 2100. (95) This is
a density of about fifty persons per square mile of
land surface on the globe, counting good and bad
land alike.
I must dissociate myself from any responsibility
for these and similar estimates. I fully realize, as do
their authors, the pitfalls inherent in such predic-
tions. Human trends being what they are and have
been in the last three hundred years, this is as good
an approximation as can be made at present, and
with all its faults it is worth considering.
The important aspect to me is that we do not
have reason to expect in the United States or in the
world a continuation of the unprecedented rate of
increase of the last three centuries, or even a con-
tinuation of the present rate of increase. Unless
population experts are all at fault, the rate of re-
HUMAN IMPLICATIONS 219
production among human animals is slowing down,
just as the rate of increase in non-human popula-
tions slows down as laboratory containers approach
an overcrowded condition. In fact, few animal popu-
lations approach the limits of their food supply in
nature.
The reasons for this are not clear, though they
appear to be connected with the ease of securing
available energy, food and shelter. As men approach
the bearable limits of these necessities of life there
occurs an increase in birth control. This is shown
in Italy, where, according to figures given in The
Statesman's Year Book, (114) despite continued
propaganda for a higher birth rate the actual num-
ber of births fell over 12 per cent from 1922 to
1936 (Figure 43). Thanks to a similar decline in
death rate the significant percentage of births which
are canceled by deaths has remained fairly steady.
In England, where there has been no great effort to
encourage population increase, the deaths in 1922
were 62 per cent of the births; in 1935 they were
81 per cent. Perhaps the success of Italian efforts is
to be measured by this comparison with England
rather than by the fact that under propagandist pres-
sure their birth rate has actually decreased. In Ger-
many, the present regime has not been in power
long enough to establish a trend. The graph (Fig-
220
THE SOCIAL LIFE OF ANIMALS
ure 43) shows that beginning in 1934 there has been
a dramatic decrease in the percentage of births can-
celed by deaths; actually there has been a decided
increase in births. Recent analyses in the American
1928 1929 1930 1931 1932 1933. 1934 1935
Fig. 43. The percentage of births that were canceled
by deaths for the given years in Italy and Germany. The
higher the trend line, the slower the population is grow-
ing and vice versa. The broken line connects the ob-
served points; the solid line shows the mathematically
smoothed trend line. (Data from The Statesman's Year
Book.)
HUMAN IMPLICATIONS 221
Journal of Sociology indicate that the present opin-
ion is that the increase in the birth rate may be
the result of a campaign against abortion which in
pre-Nazi times terminated over one-third of the
pregnancies. (58, 125) One can deduce from general
biological experience, despite the current German
data, that the population almost automatically ad-
justs numbers within its physical and biological
limitations. Doubtless eventually this mysterious
process of population adjustment will be analyzed.
At present we have made some progress toward an
understanding of the factors involved in non-human
populations, but have little objective knowledge to
report where men are concerned.
It is of course possible to increase the present
food supply of the world enormously. It has been
estimated that if our present biological knowledge
were consistently applied we could raise food enough
to supply at least ten times the present world popu-
lation, instead of the 25 per cent increase to which
we are looking forward by the year 2100. Presum-
ably by that time we shall have learned much more
than we now know about intensive methods of food
production.
Let us take one simple instance only. In the
United States we are substituting gasoline-driven
farm machinery for horse power in agricultural work.
222 THE SOCIAL LIFE OF ANIMALS
The land required to produce feed for one horse
will equally well provide food for a man. Baker,
the agricultural economist cited earlier, estimates
that the land released annually by this change in
farm technique can be turned to growing human
food almost as fast as our population is increasing.
The question seems rather one of adequate food
distribution than of shortage of food. Under con-
ditions which we can visualize at present there seems
little likelihood of a real food shortage for the world
as a whole.
If, however, these conclusions prove to be com-
pletely wrong, and the world population is now or
will become too high by biological standards, there
is still the question as to whether war is a sound
and sufficient means of controlling population
growth. The theory that war is an efficient means
of stopping the increase of mankind is so contrary
to fact that I allow myself to say No in the first
place and present the evidence later.
The immediate effect of a war upon the civilian
population is to depress the birth rate and raise the
death rate on both sides of the line, whether in the
winning or the losing nation. Figure 44, taken from
a study by Pearl on population trends during the
World War, gives these data for the unoccupied parts
HUMAN IMPLICATIONS
223
of France, for Bavaria and for England, from 1913
to 1918. (92)
In 1913 deaths and births in these parts of France
were almost equal; in 1918 there were approximately
)fT/iR
Fig. 44. The percentage which deaths were of births
steadily increased during the war years in France (non-
invaded departments), Prussia, Bavaria, England and
Wales. (From Pearl.)
two deaths for each birth. In Bavaria, in 1913, there
were five births for every three deaths; in 1918 there
were three births for every four deaths. The trend
lines in Figure 44 for these two countries run
almost parallel, though France was invaded and los-
ing in much of the fighting while Bavaria was free
from foreign troops and part of a winning nation
until near the end. As usual, analysis of such a situ-
ation is not simple. Bavaria, although enjoying the
224 THE SOCIAL LIFE OF ANIMALS
psychological advantage of belonging apparently to
the winning side, suffered the physiological disad-
vantage of an increasingly severe food shortage, while
France averaged an adequate food ration. In Eng-
land during the same time, where there was neither
invasion nor starvation, there was the same tendency
toward increase of deaths in proportion to births,
though less marked. These statistics, of course, do
not take into account the almost unprecedented
death rates in the fighting lines.
Temporarily the population growth was checked,
but almost immediately following the close of the
war the ratio of births to deaths resumed their pre-
war trend lines. Pearl, writing in 1921, (93) summed
up his study in these words: "Those persons who see
in war and pestilence any absolute solution of the
world problem of population . . . are optimists in-
deed. As a matter of fact, all history tells us, and re-
cent history fairly shouts in its emphasis, that such
events make the merest ephemeral flicker in the
steady onward march of population growth."
Fifteen years later, in 1936, (94) Pearl again wrote,
alluding particularly to the effects of wars of con-
quest by one nation to acquire the territory of an-
other: "The world problem of population and area,
however, remains unaltered in theory, though prac-
tically it will have been made worse because of the
HUMAN IMPLICATIONS 225
extravagantly wasteful destruction of real wealth that
war always causes. This is the problem that is really
serious— how can forty persons be maintained for
every square mile of land surface of the globe-
good, bad and indifferent land together? War can-
not enlarge the land surface that must support man-
kind; it has never diminished the total number of
people who want to live on it except by a tiny frac-
tion for quite a brief period. There is no way out
of the dilemma by the pathway of war."
It is a comparatively new idea that population can
be controlled at all except by famine, pestilence,
and war, which have been regarded as acts of God.
Acts of God or not, we can no longer tolerate famine
or pestilence if we have the power to prevent them;
and lacking such power we intend to get it as soon
as it is humanly possible. Among dispassionate, ex-
pert students, war has similarly lost caste as a means
of population control, though the man in the street
has not yet learned this.
Instead of the dubious check these agencies fur-
nished there is a steady turning to birth control,
even in the countries where it is most surprising to
find this. In Germany and Italy, although artificial
stimuli are being applied to keep up the birth rate,
some kind of birth control evidently is occurring.
There is significance not only in the average
226 THE SOCIAL LIFE OF ANIMALS
density of people per square mile of the earth's sur-
face, but also in the population density of the most
crowded nations. The degree of crowding in cer-
tain countries with whose problems we are familiar
is shown in the following list. The figures given are
slightly rounded statements of the average popula-
tion density per square mile of land territory. The
most densely populated countries of the world are
listed here in order (94):
COUNTRY
PEOPLE PER SQUARE MILE
1. Belgium
700
2. England and Wales
680
3. Netherlands
660
4. Japan
450
5. Germany
360
6. Italy
360
7. China (proper)
300
8. Czechoslovakia
270
For many purposes it is hardly fair to compare
the relatively small countries like Belgium and the
Netherlands with others like Japan or Italy which
are larger but contain a high percentage of waste
land. For our purposes, however, the list as it stands
is fair enough; such data represent the facts we have
to face.
At present about two and a half acres are required
HUMAN IMPLICATIONS 227
to supply food to one person, if the soil is fair to
good and the husbandry is good according to present
standards. This means that under modern condi-
tions of agriculture the upper limit of a relatively
self-contained population is about 250 people per
square mile. It will be seen that Belgium with its
700 per square mile almost triples this upper limit,
and that England and Wales and the Netherlands
more than double it. Such high population densities
can be supported by trade conducted with other
countries on a large scale. They could also, as we
have seen earlier, be supported by improved meth-
ods of agriculture. An Italian expert on populations
said in my hearing some years ago that population
pressure is not a direct cause for war, but can be
used by a clever leader to range a nation behind
aggressive policies which lead to war. In the short
run that is easier than to educate people to apply
the available knowledge which would allow Italy,
for example, to feed her present population, and
more, from the products of her own soil.
It is time now to turn to the second of the ques-
tions concerning the biological background of war.
In the light of the preceding discussion we can re-
state this question as follows: Although underlying
biological relationships do not necessarily lead to
228 THE SOCIAL LIFE OF ANIMALS
war, is not war biologically justified by the results
produced?
If war does benefit the race in distinct and unique
ways, then the biologist must favor a system of so-
ciety which will bring about the proper kind and
the correct number of wars to produce the best racial
selection. If war, on the other hand, tends toward
human deterioration then the biologist must oppose
a system of international relations based on war.
Again it is a question of evidence.
The matter of individual biological selection is
one that is fairly obvious even to the layman; and
his conclusion that the direct results of war are harm-
ful biologically has been well supported by scientists
whose interest in the subject is more inclusive than
their natural sympathy for the young men of their
acquaintance who have incurred wounds or have
been gassed or have suffered severely from some of
the typical wartime epidemic diseases. The work of
David Starr Jordan before 1914 is classic; (70, 71,
73) but the evidence furnished by the World War is
more important to us. American experience at that
time is best set forth in the slender book by Professor
Harrison Hunt (67) of Michigan State College, who
studied the records of the American army, using mod-
ern statistical methods.
He was left with no doubt that war selects the
HUMAN IMPLICATIONS 229
best of our young men for exposure to wartime haz-
ards. We have space for one bit of evidence. Hunt
found that for the drafted American army, 83 per
cent of the mentally defective were rejected; those
of normal mentality and the 17 per cent who were
only slightly subnormal were held for service. A
good geneticist would have reversed the procedure,
sending the mentally deficient out into wartime risks
and keeping the others at home to continue the
race. But this is so contrary to fact in all the stand-
ards by which armies are selected that it seems faintly
ridiculous in the telling. Personal selection, so far as
it exists in modern warfare, selects the individual to
be killed or wounded because he is physically or
mentally superior to those who are left at home. (64)
The ill effects of this selection among the young
men are evident in a nation where war losses have
been heavy, but they are less drastic for people as
a whole than they might be if it were not for various
mitigating factors. To date only half the race has
suffered in so-called civilized warfare, since women
have been exempt from actual combat. Also many
young men return who, though wounded and per-
haps otherwise handicapped, are still physically ca-
pable of passing on their gerra plasm to succeeding
generations. And even in populations badly shattered
by war most of these genetic ill effects could be ob-
230 THE SOCIAL LIFE OF ANIMALS
viated if monogamy were less of an ingrained human
practice.
The effects of severe wartime epidemics, which
are usually the cause of more deaths than the actual
fighting, are subject to the same comments; but with
these epidemics the civilian population is also di-
rectly affected, as was the case with the influenza
pandemic that swept the world in 1918, and carried
off in a day more civilians than did many spectacu-
lar air raids combined.
General epidemics tend to fall most heavily on
the old and the young; biologically we are most in-
terested in the fate of children and young people.
Disease and undernourishment drastically reduced
the younger population in places well away from the
fighting lines in the last war. Homer Folks, (47) U. S.
Red Cross commissioner, testifies that in some sec-
tions of Italy 60 per cent of the children failed to
survive wartime conditions. The children of Ger-
many and of Poland suffered greatly.
If he could know that such severe exposure elimi-
nated the relatively weaker specimens and left a
stronger, hardier race, the biologist could reconcile
himself to the death of these children, though emo-
tionally he might rebel.
But this rationalization is impossible. Study of the
after-effects of epidemics upon children (45) does
HUMAN IMPLICATIONS 23 1
not show a group of sturdy survivors, with all the
weaklings eliminated. Rather, the later history of
these children shows that they have a lower resistance
to the next severe disease that strikes them. Ap-
parently many such children, though surviving, are
weakened for some years thereafter.
Similarly, the children back of the battle lines in-
clude many whose experience left a mark, and who
recover only slowly from its injurious effects. They
were not a selected lot, and their own generation
has suffered. Fortunately all our evidence indicates
that those who survived are able to pass on their
inherited qualities unimpaired to their children; but
many are unable to provide for their families the
physical care and conditions for living which make
for the fullest development of inherited potentiali-
ties.
Perhaps a sane and cautious quotation from Pro-
fessor Holmes of California will be a fitting sum-
mary for this section. In 1921, Holmes wrote: (63)
**On the whole it is quite probable, I believe, that
the effect of military selection is harmful. ... It is
a matter of serious doubt whether the beneficial fac-
tors come near outweighing the adverse selection of
battles."
What are some of the beneficial effects which this
statement suggests may exist? One of them is that
232 THE SOCIAL LIFE OF ANIMALS
war is necessary to maintain racial vigor. This is a
matter on which statistics are not available, and on
which personal opinion must play as reasonable a
part as it can.
To me it seems a misreading of history that leads
to the justification of war as a means of keeping up
the vigor of the race. I should say, rather, that wars
have frequently revealed the loss of racial or national
vigor among a people made soft by easy living, which
in turn had been made possible, at least at times, by
a long series of successful wars of conquest.
Anyone who attempts to maintain the thesis that
wars do keep racial stocks vigorous— and there are
biologists who believe this— is troubled by the Chinese
people. This much-discussed and frequently invaded
land was populated by the forerunners of the pres-
ent Chinese during the days when Egypt, Assyria,
Babylon, Greece and Persia, to name no more, were
fighting the wars recorded in our general histories.
Those warlike peoples have lost their racial vigor
but the Chinese, who have been relatively peaceful,
have retained it. This stumbling block cannot be
removed by denying racial vigor to the Chinese; they
have, in the past, absorbed too many temporary con-
querors, and have occupied and are occupying by
peaceful penetration too much of the earth's terri-
tory, to be dismissed as a racially decadent people.
HUMAN IMPLICATIONS 233
There are anthropologists who reckon them biologi-
cally the most advanced people living today.
There is another allied but somewhat different
theory regarding the human benefits conferred by
war which holds that even though in direct personal
selection the war system is dysgenic, it does tend to
select the fittest races and nations for survival. This
theory is usually applied to European history, w^here
in the long struggle of advanced European nations
against backward poorly-equipped natives of Amer-
ica, Asia, Australia and Africa, victory has eventu-
ally rested with the Europeans. Whatever the in-
trinsic human merits of the case, a question on which
Hindus may disagree with Englishmen, there can be
no doubt that such conflicts have been won by the
nation which possesses the more modern social or-
ganization and the better gadgets with which to
fight; and the winning nation has not hesitated to
levy on the weaker one for whatever of its posses-
sions and services it could utilize for its own
advantage.
When, however, one European nation fights an-
other, as, for example, France and Germany, who
can maintain that the nation that won at Waterloo
and in 1918 is superior to the people who won at
Leipzig and Sedan? Or, to come closer home, does
the fact that the Confederacy lost the war between
234 THE SOCIAL LIFE OF ANIMALS
the States prove that the white people of the South
are racially inferior to those of the North?
Actually, of course, we are not fighting racial wars
at present. What race won the World War, or for
that matter, lost it? Modern warfare among so-called
civilized powers probably does result in victory for
superior wealth, better organization, shrewder propa-
ganda, and other social achievements, but we have
little good evidence to link these social attributes
with racial stock, in spite of contemporary German
determination to assume the connection.
Let us allow Popenoe and Johnson, (99) recog-
nized students of eugenics, to summarize this whole
inquiry into the biological justification of war. Writ-
ing in 1918, when the subject was near the top of
men's minds, they said: "When the quality of the
combatants is so high compared with the rest of the
world as during the Great War, no conceivable gains
can offset the loss. It is probably well within the facts
to assume that the period of the late war represents
a decline in inherent human quality greater than
in any similar length of time in the previous his-
tory of the world."
It seems to me that such evidence and reasoning as
I have presented indicates pretty clearly that the
present system of international relations is biologi-
cally unsound. Attempts which have been made in
HUMAN IMPLICATIONS 235
the past to lend biological respectability to the pres-
ent system by regarding it as an expression of an
inevitable struggle for existence have overlooked not
only its defects as a selecting agent but, more serious,
have often not even been conscious of the existence
of another fundamental biological principle, that of
co-operation. Is it possible to envisage a system of
international relations which will be fairly based on
both these aspects of biology?
One of the first questions to be examined is that
of the size of the co-operating unit practicable in
such a system. It is possible to make a case for the
present human social divisions, where nations of var-
ious size co-operate within their own boundaries
though competing with each other for various types
of supremacy. Within each of these nations are
graded series of groupings in great variety, which
also co-operate within and compete across their tan-
gible or intangible boundaries. Here immediately
we come across an important qualitative difference
in the competition. Within each nation this inter-
group struggle is normally carried on by approxi-
mately peaceful and orderly means. By contrast it
is accepted that the competition across national
limits, usually peaceful and orderly, may at any time
break down into the socially backward phenomenon
called war; and even in periods of peace and social
236 THE SOCIAL LIFE OF ANIMALS
progress much of the average nation's energy, wealth
and forethought is diverted to preparing for the next
war.
Peaceful intergroup competition within a nation
has come to rest, in the first place, on habit, prefer-
ence and a realization that only temporarily is an
advantage gained by violence; and, in the second
place, on a government, often set up by mutual con-
sent of the competing groups, which is strong enough
to block or stop cruder appeals to force, and which
is expected by them to do so.
The suggestion has been urgently repeated since
the time of Sully, (61) the great minister of Henry
of Navarre and France, that there should be a simi-
lar international organization. Theoretically there is
almost everything to be said for this proposal. Such
an international organization might be set up much
as the federal government of our country was
planned, to supervise the functioning of the differ-
ent states. This system calls for representative gov-
ernment, a relatively unbiased court of final judicial
appeal, and certain potential police power, which in
our American experience has been used but rarely
on a national scale.
The present League of Nations, even in its most
hopeful days, did not show more than remote pos-
sibilities of equaling on a world scale what the British
HUMAN IMPLICATIONS 237
Empire has done fairly adequately of recent years
for more than one-fourth of the earth's land area.
Any future international body which will undertake
to apply the balanced principles of struggle and co-
operation on a global basis must, among its other
qualifications, avoid certain outstanding mistakes of
the present League.
It cannot be really co-operative if it is basically a
league of victor nations formed to administer a puni-
tive peace treaty, for this is hardly a step in advance
of the time-honored national alliances for defense
and offense, which are co-operative only to be de-
structive. It must not be dominated in any depart-
ment by the representatives of any one nation, not
even when that nation is as intelligently, and shall
I say selfishly, benevolent as England and its domin-
ions today. It must be so organized as to secure and
hold adherence from the great majority of nations.
As a step toward this end, the biologist's international
system must be a dynamic organization capable of
and designed to effect changes rather than set up
to preserve any given status quo, regardless how
favorable for the predominant powers.
Biology teaches the inevitability of change, if it
teaches anything. We must have some device in our
system which will allow for needed changes, some
means of making those compromises at which the
238 THE SOCIAL LIFE OF ANIMALS
English and the French are so proficient in their in-
ternal affairs. In international as in legal circles, we
must have some peaceful means of declaring a de-
funct nation to be in fact bankrupt or unable to
manage its own business, and to distribute its assets
among the proper creditors.
When such a system is installed there will need
to be not only the means for international consulta-
tion, and a hearing for the troubles of the world;
there will also be the necessity for courts of inter-
national justice. One of these may well grow out of
the present World Court at Geneva, patterned on
the Supreme Court of this country; another might
be a development of the international court of arbi-
tration which has been located for many years at
The Hague.
At this point we come to a serious divergence of
opinion. Should these courts be supported by police
power? As a realistic biologist it seems to me that in-
ternational police force will probably be a necessity
in those cases when a nation or a section of a nation
attempts to raise itself in the peck-order of govern-
ments by direct action rather than waiting for the
results of the more just but slower pressure of world
opinion. Much of the police activities should be
limited to such duties as are now exercised by our
federal marshals, but in my judgment there would
HUMAN IMPLICATIONS 239
need to be the possibility of the use of even stronger
police pressure.
But it is certain that if an international organiza-
tion is to succeed, police power must be used very
rarely. The attempts of the British government to
coerce the American colonies or the Irish people are
conspicuous as a demonstration of the frequent fail-
ure of massed force to compose complex human
maladjustments. It is noteworthy that such enforce-
ment has not been used in the long and successful
operation of our own Supreme Court.
Practically, it is possible that nations will join in
an international enterprise which is limited to con-
sultation and judicial review of all disputes long be-
fore they will relinquish any other phase of their
jealously guarded sovereignty to such an interna-
tional organization. We may even be able to work
out a method of international co-operation based
entirely on patience, wisdom and justice, though in
the light of past experience this seems at present
unlikely.
Such a world organization will never be perfect.
Man is not. Neither is the government of Chicago, of
Illinois, of our United States. And yet who would
not prefer to live in Chicago, even back in the gang-
ster era of the nineteen-twenties, rather than in the
period of greater individual freedom for privileged
240 THE SOCIAL LIFE OF ANIMALS
people that London or Paris of the Middle Ages
afforded?
A thoughtful and sincere biologist may object that
the world is too large an area for a successful co-
operative unit; that we need units intermediate in
size to allow for human evolution those advantages
which Professor Wright has demonstrated for popu-
lations intermediate in size. To such objection one
must reply that, as to the latter point, the main-
tenance of smaller co-operative and competing units
within the larger one is part of the scheme as
sketched. And to the first, that of the great size of
the earth, it needs only to be mentioned that thanks
to recent improvements in transportation facilities.
New York is in point of time as near the Orient as
it was to Los Angeles in 1885; and there are few
places on the globe as remote from Washington as
was San Francisco before the Union Pacific Railway
was built. In transportation and communication, and
in community of essential human interests, the world
is ripe for a workable international organization.
From the standpoint of pure biology, disregarding
considerations that may seem to smack of the social
sciences, the mortal enemies of man are not his fel-
lows of another continent or race; they are the aspects
of the physical world which limit or challenge his
control, the disease germs that attack him and his
HUMAN IMPLICATIONS 24 1
domesticated plants and animals, and the insects that
carry many of these germs as well as working notable
direct injury. To the biologist this is not even the
age of man, however great his superiority in size
and intelligence; it is literally the age of insects. (7)
This is a fact which must have repeated emphasis.
In the tropics there is only the narrow strip along
the Panama Canal and similar small areas in which
man has shown the ability to compete successfully
with the insects; and the techniques of this competi-
tion are too expensive as yet to apply along the vast
rich stretches of the Orinoco River, the Amazon or
Congo; there, undoubtedly, the insects are in con-
trol. In countries like India and Russia mosquito-
borne malaria is a plague which saps the energy of
those enormous populations as it does today in our
own South.
There are good biological precedents for such
competition between different types of organisms as
that between man and insects or betw^een man and
bacteria. In fact, with almost negligible exceptions,
the only kind of mass slaughter for which there is
precedent in animal biology is found in interspecific
struggles. One species of animal may destroy another
and individuals may kill other individuals, but group
struggles to the death between numbers of the same
242 THE SOCIAL LIFE OF ANIMALS
species, such as occur in human warfare, can hardly
be found among non-human animals.
These techniques by which we can successfully
combat our enemies, the insects, and the viruses they
transport are too expensive for the world today.
They are too expensive because even the peaceful
nations are using so much of their resources for buy-
ing and building armament on an unprecedented
scale, apparently to make one more experimental test
of the fact that war is biologically indefensible.
In our struggles with our physical environment,
with disease germs and insects, we have ample op-
portunity for the struggle for existence, and stimu-
lus enough to apply to the limit the principle of
co-operation.
Unconsciously or consciously, the innate urge to-
ward co-operation appears even under circumstances
where it would seem least likely to be fostered.
Even in the most seriously war-torn countries, as
in Spain today, when one is withdrawn from the ac-
tual scene of battle one finds the common people en-
gaged as best they can in their normal activities of
providing food, clothing and shelter for themselves
and their families, with the ineradicable drive to-
ward constructive co-operation that we have found
evident throughout the animal kingdom. Such co-
operative activity will reach through a family, from
HUMAN IMPLICATIONS 243
family to family, from city to city and even across
frontiers.
These normal activities can be wiped out in a few
minutes by the exaggerated expression of the struggle
for existence which we call war, extended beyond
all biological justification and become, as Malinowski
has said, "nothing but an unmitigated disease of
civilization." (78)
It is a disease of long standing which even under
most favorable conditions we must not expect to
see cured overnight; but the outlook is not without
hope. There seems to be no inherent biological rea-
son why man cannot learn to extend the principle of
co-operation as fully through the field of interna-
tional relations as he has already done in his more
personal affairs. In addition to the unconscious evo-
lutionary forces that play on man as well as on other
animals, he has to some extent the opportunity of
consciously directing his own social evolution. Un-
like ants or chickens or fishes, man is not bound
over to form castes or peck-orders or schools, or to
wait for a reshuffling of hereditary genes before he
can discontinue behavior which tends toward the
destruction of his species.
VIII.
Social Transitions
WHEN DOES an animal group become truly social?
This question has already arisen in preceding chap-
ters and is difficult for a thoughtful biologist to an-
swer with confidence.
One school, now happily small, regards society as
beginning when animals first display a social in-
stinct. (16) By this they probably mean that social
animals have inherited a behavior pattern that
causes them to live together with others of their kind
in more or less closely co-operative units. Others
consider that animals are social when they carry on
group life in which there is clear evidence of a divi-
sion of labor. (42) There is also the frequent sug-
gestion that only those animals are truly social whose
behavior is an extension, directly or indirectly, of
familial behavior. (119)
For myself, I regard those groups in which ani-
mals confer distinct survival values upon each other
as being at least partially social; this is the concep-
tion that has most often appeared in these pages. (3)
244
SOCIAL TRANSITIONS 245
And from a still different point of view, those who
would stretch the idea of social living rather widely
would say, as I have indicated in Chapter V, that
when animals behave differently in the presence of
others than they would if alone, they are to that
extent social. (115)
These ideas concerning what constitutes a proper
definition of animal societies, while not necessarily
mutually exclusive, are sufficiently different to raise
difficulties when one tries to examine critically the
useful general concept of social life; it will be profit-
able to study some of them separately.
As to the first definition, that social life must be
limited to those animals that possess a social instinct,
an inherited behavior pattern, it is hard to demon-
strate beyond reasonable doubt that many patterns
of social behavior are in fact inherited. Is the
tendency of many fishes to form closely-knit schools
inherited or an early-conditioned bit of behavior?
There is some evidence that it is inherited, but we
are not yet sure of it. But if it were granted that
such schooling tendencies are innate, it would not
necessarily follow that they are instinctive. There are
different degrees of complication of inherited be-
havior patterns, from the relatively simple reflex ac-
tion of an unborn embryo to the complex mating
behavior shown, for example, by some insects and
246 THE SOCIAL LIFE OF ANIMALS
by rats. The exact determination of the place in this
line of increasing complexity at which an action
ceases to be a simple reflex and becomes a more
elaborate tropism, or the point at which the tropism
gives way to an instinct, has never been made. That
is, we do not know just how far down in develop-
ing patterns instinctive behavior extends.
There is the added complication that the word
"instinct" has been loosely used. The most workable
definition that I have arrived at is a modification of
an older one of Wheeler's: An instinct is a com-
plicated reaction which an animal gives when it re-
acts as a whole and as a representative of a species
rather than as an individual, which is not improved
by experience, and which has an end or purpose of
which the animal cannot be aware. Too frequently
the word has been applied to any bit of behavior
whose origin and motivation the observer did not
understand, with the unfortunate paradoxical im-
plications that thereby the action was explained and
at the same time could not be further explained.
As a result of this uncritical usage many careful
workers disapprove employing the word under any
conditions, and particularly in the field of social
activities.
In recent years some students of social life have
attempted to avoid the term "social instinct," while
SOCIAL TRANSITIONS 247
employing the same fundamental idea under the
thin disguise of "social appetite," (122) "social drive,"
or "group interattraction," (100) which is apparently
understood as inherited. These contributions to a
more picturesque language do not necessarily ad-
vance our understanding of social behavior.
Still others sincerely believe that fiehavior patterns
are not inherited, which seems to me a clearly un-
tenable position. But however strong my belief in
the actual inheritance of social behavior I do not
consider it helpful to make the possession of such an
inheritance the major criterion of social living; it
is not a practical working test as to what constitutes
social life.
If division of labor be used as a touchstone the
same type of difficulty arises. We do not know how
to determine when such a division becomes suffi-
ciently general to merit being called a social attribute
in the stricter sense in which we are now using the
term. For example, there is a division of labor which
is associated with sex and which is almost as exten-
sive as sex itself. When does this particular division
of labor cease to be merely an expression of sex and
become social in the commonly accepted use of the
word?
The mention of sex brings up again another im-
portant definition of social life among animals which
248 THE SOCIAL LIFE OF ANIMALS
has already been listed. This states that only those
groups which have grown out of the persistence of
sexual and more especially partial or completely
familial relations are truly social. This point of view
has been touched upon with some sympathy in the
first chapter. There is an important relationship
which underlies this definition; many highly organ-
ized social groups do develop from the continuation
and extension of family ties. But though this con-
dition has given rise to many of the better devel-
oped social units, care must be taken not to regard
its presence as the essential difference between the
social and the sub-social. As Professor Child (32) has
suggested, boys' gangs, girls' cliques, and men's and
women's clubs present difficulties to one who wishes
to define all societies as extensions of familial rela-
tionships. It is quite possible to regard such social
phenomena as expressions of other aspects of the
social urge which have developed independently of
paternal or fraternal interactions. There are counter-
parts of these human groups among other animals,
as well as counterparts of the extensions of family
life. The overnight aggregations of male robins, the
long-continuing stag parties of male deer outside the
short rutting season, (38) the flocks of mixed species
of birds common in tropical regions (Beebe tells of
one made up of twenty-eight individuals represent-
SOCIAL TRANSITIONS 249
ing twenty-three species, (24) ) schools of fishes, and
the swarms of animals spoken of in the second chap-
ter, all of these instances test and stretch in varied
ways the idea that only those continuing aggrega-
tions of animals which grow out of sexual and
familial interrelations are truly social.
Inherited behavior patterns, the forerunners of
instincts, and sexual differences extend down to the
protozoa; so do continuing family groups, especially
in the form of structurally connected colonial or-
ganisms. Group survival values are present in groups
of organisms in which sex has not yet evolved, as
well as among those in which sex is elaborately de-
veloped. In the light of such considerations it be-
comes exceedingly difficult to establish any one line
above which life is to be regarded as truly social
and below which we have only differing degrees of
sub-social relations. Here, as happens so frequently
in biology, we are confronted with a gradual devel-
opment of real differences without being able to
put a finger with surety on any one clearly defined
break in the continuity. The slow accumulation of
more and more social tendencies leads finally by
small steps to something that is apparently different.
If we disregard the intermediate stages the differ-
ence may appear pronounced, but if we focus on
these intermediates it will be only for the sake of
250 THE SOCIAL LIFE OF ANIMALS
convenience that we interrupt the connecting chain
of events at some comparatively conspicuous link
and arbitrarily make this the dividing point, when
one is needed, between the more and the less social.
It must be recognized that any such division is a
matter of convenience rather than a natural break in
the development from mass or simple group behavior
to highly evolved social life.
For our purpose in the present account it is suffi-
cient to recognize that the well-integrated social
systems of man and other mammals, of bird flocks
and of insect colonies, exhibit among them the
highest expressions of social abilities that have
evolved. In the range of social development shown
in these animals we find attributes that are truly
social in the most exclusive use of the word. But
these highest expressions of social living have their
roots in tendencies that in the form of unconscious
co-operation accompany animal aggregations extend-
ing throughout the whole animal world, as well as
to some extent among plants. Conceding then the
difficulties in the way of making any exact definition
of social behavior, I wish to present some of the
social implications of mass physiology, particularly
among well-integrated societies of animals.
One of the characteristics of social life among the
insects is the presence of castes (121) which perform
SOCIAL TRANSITIONS 25 1
different functions within the colony. With many
social insects the division of labor has developed
to such an extent that the animals which do dif-
ferent work have bodies that are more or less struc-
turally appropriate to their principal tasks. The
reproductive female has a greatly enlarged ab-
domen; the soldier grows up to possess large jaws
and heavy armor or other protective and attacking
devices; a worker may be large or small or medium
in size, according as its size will best suit for some
of the varied tasks necessary for the life of the whole
colony. The situation is greatly different from that
among human social castes, where a member of the
aristocracy may be as husky of body and as empty
of mind as the most menial of the working caste.
The only physically distinct castes to be found in
man and the higher vertebrates are those associated
with sex. In sexual forms there is always a division
of labor with regard to the primary sexual functions
except in those rare cases, usually low in the evo-
lutionary scale, which at one and the same time are
both male and female. With many, aside from pro-
ducing eggs rather than sperm, it is difficult to find
a division of labor or of appearance between the
sexes. With others, particularly among the more
specialized animals, there are differences in sexual
behavior and responsibilities which are associated
252 THE SOCIAL LIFE OF ANIMALS
with the more fundamental distinctions of sex. Fre-
quently, as in man, these differences have developed
into fairly distinct behavior patterns for the two
sexes, until each sex is practically a distinct caste,
almost in the sense used in discussing castes among
the social insects.
Sex is usually determined by differences in he-
redity which are associated with the combination of
chromosomes (37) and of the bearers of heredity
(genes) that are found in the sperm and egg whose
union gives rise to the new individual. Such deter-
minations occur at the time of fertilization and sex
is normally unaltered thereafter.
Exceptions occur which demonstrate that for cer-
tain animals this normal means of sex determination
can be overruled by environmental differences. Many
of these cases are interesting and significant but their
full consideration here would draw us off the main
thread of our present discussion. We shall follow
only those instances in which changes in sex are
associated with the near-by presence of other indi-
viduals, considering here two widely differing cases
which have been carefully investigated in recent
years.
Professor Coe (35) of Yale has spent much of his
time studying the sex ratios and sexual changes in
oysters, clams, marine snails and other related forms.
SOCIAL TRANSITIONS 253
In many of these mollusks he has found that the sex
ratios vary greatly in different environments, and
has reached the conclusion that frequently among
these animals the expression of an innate sexual
tendency may be in part suppressed or stimulated,
as the case may be, by the environment in which
any given animal is living.
A pertinent case is that of a set of marine snails
of the genus Crepidula. Three of these "boat-shell"
snails are common animals in the coastal waters of
southern New England. Their sexual history follows
similar outlines. After a juvenile period which is
essentially asexual, the growing Crepidula becomes
first a male and then later, sometimes only at long
last, it transforms into a female. A typical species to
follow through this transformation is Crepidula for-
nicata.
When young, these animals move about, but as
they become older and larger they settle down in
one place on a wharf piling or a rock or another
shell. If the larger, older animals are broken loose
the soft parts are usually destroyed by some predator
before they can reattach themselves, leaving behind
the relatively heavy shell. Frequently they form
large chains of individuals, of which a simple exam-
ple is shown in Figure 45. The large, bottom snail
254 THE SOCIAL LIFE OF ANIMALS
is dead. Attached to its shell is a large female which
in summer actively produces eggs. Above her are
two individuals that are undergoing transformation
from male to female. Scattered about over these are
Fig. 45. Crepidula fornicata. (A) A basal female is
attached to a dead shell (D); two individuals are in tran-
sition stages and there is one male at the apex; three
motile supplementary males are in mating position on
the lower transition individual. (B) same group from the
left side. (From Coe.)
four smaller snails which are still functional males
and which can and do move about. Each male has
a long slender penis by means of which he transfers
sperm from his body to an appropriate receptacle
in the body of the female. Several males may par-
ticipate in the insemination of a single female.
The growth of these snails is fairly rapid. A young
snail hatched out early in the summer may, before
autumn, become a functional male about 16 mm.
long, which is about two-fifths the size of a fully
SOCIAL TRANSITIONS 255
adult female; during the following year he will
probably transform into a female.
The relationships which Dr. Coe observed at
Woods Hole may be summarized briefly. Some two
hundred young males were taken from their normal
surroundings and placed in separate containers in
the laboratory. Two months later only ii per cent
were still functional males; 15 per cent had trans-
formed completely into functional females and the
other 74 per cent were on their way in that direc-
tion. Random collections of snails of similar sizes
which had been left alone in their natural associa-
tions showed that 85 per cent were still functional
males and only 3 per cent had fully changed into
females.
Coe summarizes his work with this and the other
Crepidulas as follows: "There is no doubt but that
in each of these three species of Crepidula stable
environmental conditions tend to prolong the male
phase of these individuals that are suitably mated
and sedentary." These points are further illustrated
in his diagram, a part of which is reproduced in
Figure 46.
There is evidence from the earlier work of other
observers, (54, 87) which these recent studies do not
entirely replace, that association with a female is
important for the full realization of the male con-
2r.6
THE SOCIAL LIFE OF ANIMALS
dition as well as for its prolongation. With these
snails the tendency to become first a male and later
a female is probably determined by heredity, al-
though the hereditary mechanism which promotes
such a shift is at present unknown. The point of
interest for this discussion is that the association
CFORNICATA
Fig. 46. As Crepidula fornicata gets older and larger
it passes successively from the sexually immature
through the male on into a final female stage. Mated
males retain that stage longer than if actively motile.
(From Coe.)
with others, especially among mated males, tends to
postpone transformation to the opposite sex.
Some cases are known in which the presence of
other animals of the same species determines the
sex. One of the most thoroughly studied is that of
the worm Bonellia, (21) in which the sexually un-
differentiated larva does not, in nature, become the
small parasitic male unless it is associated with the
large female.
Among certain nematode worms which are para-
sitic in insects, if few eggs are introduced into, for
example, grasshoppers, (3) most of the resulting
SOCIAL TRANSITIONS 257
nematode parasites are females; but if many eggs
are fed, the nematodes that hatch are almost all
males. The results are not to be ascribed to a differ-
ential death rate, for approximately 75 per cent of
the eggs develop in both cases.
In Crepidula and Bonellia and nematodes, both
males and females are always present in a popula-
tion, though in differing ratios. In cladocerans, how-
ever, of which Daphnia is an example, the species
may be carried along for many generations by the
females alone. They produce eggs which do not re-
quire fertilization, but which develop directly into
females that again produce other females like them-
selves. In these cladocerans the race is usually made
up of females alone, but at times there is an out-
break of sexuality; males and sexual females appear
and the fertilized eggs which result from their union
are more resistant to adverse conditions than those
which are ordinarily produced and which require
no fertilization. These resistant eggs enable the spe-
cies to survive times of environmental stress, such as
winter's ice or the drying-up of the ponds in which
these small crustaceans live.
In one species of Moina, (5) which has been
much studied by the biologists at Brown University,
crowding of the females is an effective method of
bringing on the outbreak of males and sexual fe-
258 THE SOCIAL LIFE OF ANIMALS
males, so that overcrowding may be rated as a time
of environmental stress. Either by the shortage of
food, by the accumulation of waste products, or
from some other cause, the association of many fe-
male cladocerans together results in the production
of eggs which have a different prospective potency
from those the same females, uncrowded, would
produce; and sexual males and females are the result.
It is evident from these varying examples that
even the fundamental matter of sex, with the caste*
like divisions of labor that result from two sexes,
may be determined by the close association of ani-
mals of the same species. There is some reason,
though perhaps it is slight, for suggesting as in
Chapter III that sex itself may have grown origi-
nally out of mutual acceleration in division rates
when two or more primitive organisms were in close
contact in small space. The whole matter of sex may
hark back to some of the basic aspects of mass physi-
ology which were set forth earlier in this book.
Sex in its different aspects plays a highly impor-
tant role in the social affairs of animals. It is inter-
esting to find that this fundamental cleavage through
so much of animal life can at times be controlled
by group relationships. Such considerations serve
again to emphasize the difficulty of drawing a hard
SOCIAL TRANSITIONS 259
and fast line, or even a fairly distinct band between
social and sub-social living.
One phase of the social implications of sex has
escaped general comment. I heard it first mentioned
by Professor Wheeler. (123) Apparently when there
is a social difference between the sexes it is the fe-
males that are the more and the males the less social;
and the few striking exceptions only confirm the
rule.
Among the social ants, bees and wasps the normal
affairs of the colony are carried on by the females.
They produce males only when they are needed to
fecundate the young virgin females at the time of
their nuptial flight. The males contribute nothing
to the protection, feeding or housing of the colony;
after their one sexual activity they die or are killed
off, and the females which are lucky enough to
secure a good nesting site carry on with their female
offspring until sexual reproduction again becomes
the order of the day (Figure 47).
With many of the herds of mammals, the main
duties of communal life are borne by the females.
They protect and rear the young and herd together
to protect each other. The males keep to themselves
except during the relatively brief period of the
sexual rut. Even when they join the main herds, as
in the case of the Scottish red deer, frequently the
26o THE SOCIAL LIFE OF ANIMALS
males do not fuse with the others. When danger ap-
pears during the rut, the stags make off and rejoin
the females when it is past. After a male is sexually
spent, frequently before the close of the breeding
season, he withdraws, and the spent males form stag
Fig. 47. Castes of the common honey-bee; a, queen; b,
male (drone); c, worker. (After Phillips.)
parties which are distinctly less social than the bands
of females.
In commenting on the relative sociability of the
sexes among red deer, Darling says: (38) "Matriarchy
makes for gregariousness and family cohesion. The
patriarchal group (among deer) can never be large,
for however attentively the male may care for his
group he is never selfless. Sexual jealousy is always
ready to impinge on social relations leading to gre-
gariousness. ... I contend that the matriarchal sys-
tem in animal life, being selfless, is a move toward
the development of an ethical system."
SOCIAL TRANSITIONS 26 1
The flocks of male birds whose social organization
we have studied in Chapter VI are more combative
than the females. The human male writes the great
poems, builds the great bridges, performs the out-
standing scientific research; but he is also the crim-
inal, the war-maker, the disturber of the peace. It
is the human female that is the highly social force
with our species, and in this we are again similar
to the others mentioned.
Among the social animals only the termites have
fully socialized males; with them the male reproduc-
tives consort with the female throughout life. Half
the soldiers are males and the other half are females,
and so are the workers. Termites are lowly insects,
but in this one trait they lead the world. No one
knows how the socialization of male termites was
brought about, and if we should learn their secret
it probably could not be applied directly to human
affairs.
When we turn from the far-reaching division of
most animals into two sexual castes to explore the
origin of the more specialized castes of insects, we
find two different essential kinds, the reproductives
and the sterile types. With bees, ants and wasps, for
example, the usual reproductive females can pro-
duce eggs without being fertilized by a sperma-
tozoan. Such eggs always give rise to males. From
262 THE SOCIAL LIFE OF ANIMALS
the Store of sperm which she received in the nuptial
flight the same female can allow her eggs to be fer-
tilized; such fertilized eggs become females.
We have seen the comparative unimportance of
the males. Although the active colony is usually
composed of females only, these may be quite dif-
ferent in appearance and function. Typically there
are the reproductive females and the sterile ones.
Among the ants the sterile females are divided into
the protective soldiers, whose main function is to
protect the colony from the attack of other species
of animals, and the workers proper. The ant work-
ers are subdivided on the basis of size (Figure 48).
Professor Wheeler made the study of these social
insects, particularly the ants, his life work. In a
small book, published in 1937 after his death, he
reaffirmed his belief that ants and bees have evolved
from ancestral wasps, and that each has developed
the caste system independently. (124)
With bees and wasps, whether a given fertilized
egg is to produce a worker or a sexual "queen," bet-
ter called a reproductive female, depends on the
treatment and food which is given to the grub
which hatches from the egg. If she receives plenty
of food and is given space in which to grow she
becomes fully matured sexually; if fed less and kept
more crowded she becomes an incomplete female
Fig. 48. Some ant castes: a, soldier; b, form interme-
diate between soldier and worker; c, worker; d, form in-
termediate between soldier and worker; e, queen that
has shed her wings; i, winged mal^. (After Wheeler.)
264 THE SOCIAL LIFE OF ANIMALS
and is known as a worker. Apparently the funda-
mental difference can be brought about only by the
treatment which the developing grub receives after
hatching, and is not a matter of heredity. Just how
the workers are stimulated to give one or more grubs
the treatment that will allow them to develop their
full reproductive capacities is not fully known. If,
however, the queen bee dies or is removed from the
colony, workers will start enlarging one or more of
the cells which contain developing grubs, change
their care and feeding and so allow them to trans-
form into fertile reproductives. Perhaps they are
kept from doing so when a queen is present by some-
thing like a social hormone, which there is good rea-
son for thinking is produced by the even more social
termites.
The mechanism which results in caste formation
among ants need not be the same as that in wasps
and bees, since it is generally conceded that they
had a separate social evolution. For years two theo-
ries have been promoted as to how ant castes came
into being. One group of students thought that ant
castes were determined as were those of bees and
wasps, by care and food; another group w^as equally
sure that the differences were hereditary. After con-
fessedly wavering between the two views in his long
study of ants. Professor Wheeler in his posthumous
SOCIAL TRANSITIONS 265
book presents the evidence which finally caused him
to decide that with ants the whole matter of caste
formation is primarily controlled by heredity.
This is a question which will undoubtedly occupy
students of ants for years to come. The evidence is
not all in, and the fact that at present it tends to
indicate that ant castes are determined by heredity
makes all the more interesting the instances in three
separate kinds of social insects of the apparent evo-
lution of group control of castes after the hatching
of the egg. To this hasty sketch of the operation of
group determination of caste in wasps and bees may
be added that of termites.
The bees and their allies belong to one of the
most specialized of insect orders, so that they are
assigned a high position in the evolutionary tree of
that class of animals. The termites, miscalled white
ants, belong to a relatively unspecialized insect order
related to the cockroaches, and stand low in the
evolutionary scale among the insects. They have,
however, reached a high state of social development.
Unlike bees, ants and wasps, the colony, as we
have said, is at all times composed of males and fe-
males in approximately equal numbers. There are
male and female reproductives. of which three dif-
ferent kinds are known; these are the so-called first
form which have wings for a time and engage in a
266 THE SOCIAL LIFE OF ANIMALS
nuptial flight, second form reproductives with wing
buds, and third form, which are wingless; and there
are the sterile workers and soldiers in which both
sexes are also represented equally. The colony is
usually composed of reproductives of some one sort,
and the two sterile castes (Plate V).
The controversy as to whether caste formation is
a result of heredity or of the social environment has
been as intense with students of termites as among
students of ants. The trend of present information
tends to support the theory of control by the environ-
ment. (27, 75) A certain California termite called
Zootermopsis has reproductives and soldiers in its
colonies, but no workers in the accepted sense of the
term. Their place is taken by the younger nymphs,
all of which have the possibility of developing into
one of the reproductive grades or into soldiers.
When Dr. Castle of the University of California (27)
set up experimental colonies of nymphs alone, he ob-
tained in due time one or more pairs of reproduc-
tives. If the small experimental colony lacked a fer-
tile male, one of the nymphs developed into that; if
a fertile female was lacking and a male was placed
in the colony, a nymph developed into a fertile fe-
male. If the nymphs in a colony that lacked both
males and females were fed on filter-paper which
contained an extract of fertile females made with
PLATE V. Winged reprodiiciixe caste, soldiers and
workers of a termite from British Gtiiana. This is one
of the largest species of termites and is shown life-size.
A, winged reprodiictives; B, soldiers; C, workers. (Pho-
tograph by AVilliam Beebe.)
SOCIAL TRANSITIONS 267
alcohol or ether, the males appeared at the usual
time, but the females were delayed by twelve or six-
teen days on the average.
Ordinarily in Zootermopsis only one soldier ap-
pears in the first year of the life of the colony. By
removing the soldier as soon as it appeared in the
experimental colony it was possible to get as many
as six soldiers within the time that would ordinarily
have yielded only one.
In explanation of these and other similar data
Dr. Castle expresses his opinion that at the time of
hatching all nymphs possess three sets of possibili-
ties to the same degree; namely, they may become
sexually mature though wingless, they may become
winged and sexually mature, or they may become
soldiers. At some stage these chances are narrowed
to two possibilities: the nymph may become sexu-
ally mature or it may develop into a sterile soldier.
Since the reproductive possibility is present in all
nymphs and since its expression is inhibited by a
substance produced by a functional reproductive and
eaten by the nymphs, the absence of functional re-
productives would allow this potential power to ex-
press itself. Just what determines that one of the
first small lot of eggs will become a soldier is not
known, but it can easily be seen that when one
soldier has started to develop it too may give off an
268 THE SOCIAL LIFE OF ANIMALS
inhibiting influence which prevents other nymphs
from becoming soldiers. In the normal course of
events a second soldier appears only when the colony
has become sufficiently numerous so that the soldier-
inhibiting substance is spread among so many that
the effect on any one nymph is weakened; and some-
thing of the same effect of numbers may explain
why, in a large colony, many nymphs develop at
times into sexually mature and winged forms.
There seems to be a relation to the more gen-
eralized situation noted earlier. When many animals
are exposed together to a given amount of alcohol
or some other toxic material, no one of the many
may receive any overdose, as will certainly happen
when one or a few individuals meet the full effect
of the poison. This type of relatively simple mass
effect, first discovered in experiments on group phys-
iology among animals that at the most are only
partially socialized, apparently turns out to be an
important mechanism in regulating caste formation
among these highly social termites; and some simi-
lar mechanism may control the activity of worker
bees in producing new queens. It is true that the
control of caste production is probably not the
simplest form of physiological mass action, for the
insects may from time to time become less sensitive
to such inhibition. At these times, many of the
SOCIAL TRANSITIONS 269
nymphs may develop into the winged reproductives
that swarm forth in the nuptial flight.
As many know, most termites eat wood which,
paradoxically enough, they are unable to digest
although they do obtain their nourishment from it.
The answer to this riddle is that the termites harbor
in their alimentary canals several species of flagel-
late protozoans which can and do change the wood
into substances which both termites and these flagel-
lates find highly nutritious.
From many structural relationships we know that
termites are close relatives of cockroaches, and studies
by Dr. Cleveland of Harvard (34) have shown how
the termite societies may have arisen from the much
less social cockroaches. Here we have an example of
one of the many possible connections between highly
developed social life and the less social state illus-
trated by the mass physiology characteristic of animal
aggregations.
Cryptocercus is a wood-eating cockroach which is
found in decaying wood of the forests of the Ap-
palachian mountains from Pennsylvania to Georgia,
and along the coastal mountains in the northwestern
part of the United States. Like their relatives, the
termites, these cockroaches feed on wood, and also
like the termites they harbor wood-digesting pro-
tozoans in their alimentary tract. These wood roaches
2^0 THE SOCIAL LIFE OF ANIMALS
and many termites cannot live long if deprived of
their associated protozoa, as can be done by appropri-
ate treatment in the laboratory.
The young of both cockroaches and termites hatch
out without these essential protozoans. The termites
obtain theirs by swallowing a drop of liquid which
has just emerged from the anal opening of another
termite; the cockroaches get their protozoans by eat-
ing the pellets passed from the alimentary tract of
molting individuals. Once a cockroach obtains a
good supply it renews itself. One such cockroach
or a pair can emigrate to a new log and live there
for a lifetime. Since, however, adult cockroaches do
not molt, the young of such an isolated pair, when
hatched, could not receive the so-necessary intestinal
protozoa, and hence a pair, if isolated, could not
found a new colony. Actually the eggs hatch at just
about the time of the annual molting season when
the young growing roaches cast their outer covering
and a part of the lining of their alimentary tract.
At this time the newly hatched young can obtain
protozoa readily and thereafter they retain them.
The habit of living together is necessary in order
that the growing, molting young may transmit their
protozoa to the newly hatched nymphs.
The social situation is still more necessary for the
termites. With them all the intestinal protozoans are
SOCIAL TRANSITIONS 27 1
lost with each molt, and each time that happens
each newly molted individual must obtain some of
the protozoans from another member of the colony
or it will starve. The newly hatched termites often
obtain protozoa before they are twenty-four hours
old, and an artificially defaunated termite, if allowed
to associate with his normal fellows, is reinfected
within a few days. With the termites, colony life is
an absolute essential and only the winged males and
females, the first form reproductives already infected
with protozoans before taking the nuptial flight, can
even start a colony without the presence of others to
carry the needed cultures of protozoans.
Many cockroaches which neither eat wood nor
harbor wood-digesting protozoans reproduce so
rapidly that given good hiding places and plenty of
food they aggregate in large numbers, as many
housewives know. These cockroach aggregations,
which appear to be formed as a result of tropistic
reactions to the environment, accompanied by tol-
eration for the presence of others, permitted the
wood-roach Cryptocercus to develop the habit of
passing protozoa from one individual to another, and
so began the long evolution which has resulted in the
highly adapted, wood-eating roaches found today.
The same basic adaptation allowed their relatives,
the termites, to start on the much longer road they
27^ THE SOCIAL LIFE OF ANIMALS
have traveled to reach their present state of highly
developed social life.
We cannot outline the steps taken very closely, but
it would seem that in this cockroach-termite stock
aggregations allowed aspects of mass physiology to
develop which in turn permitted a closely knit and
varied social evolution. This is about as near as we
have yet been able to come to charting a direct and
obvious truly social development from a slightly so-
cial or sub-social animal aggregation.
Among grasshoppers crowding can produce obvi-
ous structural changes (Figure 49). Certain species of
grasshoppers found in semi-arid regions, such as
those of South Africa, have two phases (5) that are
quite distinct from each other. The phases are suffi-
ciently different so that in the past they have been
described as being different species. There is at
present much evidence which indicates that the
phase solitaria can be turned into phase gregaria by
crowding the young nymphs into dense masses. The
opposite transformation may take place when the
nymphs of phase gregaria are reared under un-
crowded conditions. The differences between the two
extend into color, form and size.
Similarly plant-lice, which are also called aphids,
exist in wdnged and wingless forms which tend to
alternate. When the wingless aphids have approxi-
1^.
Fig. 49. The five upper nymphs (1-5) and the lowest
adult belong to the swarm phase; the others (6-11) show
different aspects of the solitary phase of the brown
locust (Locustana pardalina) of SoTith Africa. This is a
black-and-white copy of a color plate by Faure. Black
here represents black or bluish-black in the grasshop-
pers; heavy stippling represents dark brown; light stip-
pling represents light or golden-brown except in parts
of Nos. 7 and 9 which are green.
274 THE SOCIAL LIFE OF ANIMALS
mately exhausted the juices from one food plant the
next generation appears with wings; in flying about,
some of them will usually find a new and suitable
food plant where they can settle and carry on. With
some species one of the most effective ways of keep-
ing wings from developing is to isolate the individ-
ual aphids and, conversely, one of the best recipes
for obtaining winged forms is to allow them to be-
come crowded. (104)
These distinctly different types of grasshoppers
and aphids roughly suggest the structural differences
between the castes of social insects, just as compari-
son was suggested between the structural differences
of caste and of sex. The resemblance is so close that
the line cannot be drawn between its manifestations
in social and infrasocial animals. Not only that, but
the mechanisms by which the castes are produced
appear in many instances to be like those which may
occur when animals are aggregated together, even
though the aggregations are below the level usually
regarded as marking the lower limit of truly social
life.
And since no one has yet demonstrated the exist-
ence of truly asocial animals it is impossible to define
the lower limits of sub-social living. All that can be
found is a gradual development of social attributes,
suggesting, as has been emphasized throughout this
SOCIAL TRANSITIONS 275
book, a substratum of social tendencies that extends
throughout the entire animal kingdom. From this
substratum social life rises by the operation of dif-
ferent mechanisms and with various forms of expres-
sion until it reaches its present climax in vertebrates
and insects. Always it is based on phases of mass
physiology and social biology which taken alone seem
to be social by implication only.
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Index
^
Aggregations, in nature, 32;
hibernating, 32; breeding,
33; migrating, 33, 35, 37;
various examples, 34; co-
lonial animals, 41; forced,
42; feeding, 44; overnight,
46, 248; relation to social
life, 49, 272
Alcohol, mass protection from,
52
Alverdes, F., 29
Ancestral tree of animals, 86,
87
Antelopes, 37
Ants, 26, 32; effect of num-
bers on digging, 139; im-
portance of females, 259;
castes, 262, 265
Aphids, 272
Appetite, social, 44, 47, 247
Arhacia eggs, 69; spermatozoa,
69, 83; effect of numbers on
rate of cleavage, 71; effect
of extracts, 74
Bacteria, mass protection, 67;
food for protozoa, 77
Baker, O. E., 217
Bats, 36
Bavaria, population trend,
223
Beebe, William, 248
Bees, 26, 260, 262, 264, 265;
solitary, 46; importance,
259; castes, 260
Beetles, hibernation, 32
Behavior, of isopods, 20;
group, §2, 133; social cri-
teria of, 173
Belgium, population, 226, 227
Bennet, Mary, 185
Birds, 33, 46, 47, 48, 88, 110,
134' 155' 175' 206, 250, 261
Birthrate, 219
Bison, 38
Bonellia, 256
Bowen, Edith, 92
Breeding season, 33, 133
Butterflies, overnight aggrega-
tions, 46
Calcium, protective value, 65
Canaries, social order, 191,
193, 207
Caribou, 37
Caste, 250, 274
Castle, G. B., 266, 267
Chapman, Frank M., 134
Chapman, R. N., 104
Chen, S. C, 139
Chickens, group stimulation,
135; social order, 176, 190,
193, 207; IQ, 192
Child, C. M., 58, 248
290
INDEX
Children, effect of class size,
143; in wartime, 230
China, population, 226; racial
vigor, 232
Cladocera, sex determination,
257
Class size, effect on rate of
learning, 142
Cleveland, L. R., 269
Cockroaches, effect of num-
bers on rate of learning,
149; related to termites,
265, 269
Coe, W. R., 252
Collias, N., 185
Colloidal silver, mass protec-
tion from, 53, 56
Colonial organisms, 41
Community, ecological, 38
Confusion effect, 139
Conditioned water, 64, 92
Co-operation, history, 23, 31;
ecological, 40; voluntary,
42; evidence for, 49, 50; un-
conscious, 88, 133; con-
scious, 209; principle of,
209, 211, 242, 243
Copepods, 35
Crepidula, 253
Crowding, harmful effects, 31,
50
Ctenophores, 35
Czechoslovakia, population,
227
Cyprinodon, learning, 164
Daphnia, mass protection, 57,
139; food for fish, 137; sex
determination, 257
Darling, E. Fraser, 111, 260
Deegener, P., 28
Deer, 48, 248, 259, 260
Despotism, 185, 208
Dionne quintuplets, 201, 207
Disease in wartime, 224, 225,
228, 230, 231
Division of labor, 32, 247, 251
Dominance, qualities causing,
190; relation to breeding
cycle, 194
Drosophila, effect of numbers
on rate of reproduction,
103
Eggs, sea-urchin, 69
Elephants, minimal popula-
tion, 108
Ellis, Havelock, 24
Emigration, 122, 126, 131
Empedocles, 23
England, population trend,
219, 223, 226, 227
Espinas, A. V., 25, 28
Euglena, 34
Evans, Gertrude, 73, 92
Evolution, course of, 86, 87;
effect of numbers on rate
of, 118; Lamar ckian, 118
Family, as origin of society,
47, 244, 248
Finkel, Asher, 92
Fish, schools, 48; mass pro-
tection, 53, 56, 68; effect of
crowding on growth, 92; on
amount of food taken, 136;
on learning, 158; leader-
ship, 166; imitation, 170
Fischel, W., 196
INDEX
291
Flocks of birds, breeding, 111;
social organization, 175,
206; leadership in, 196;
wheeling flight, 198; of
mixed species, 197, 248
Folks, Homer, 230
Forced movements, 43. (See
Tropism)
France, population trend, 223
Fresh water, mass protection
from, 63
Fundulus, learning, 164
Gates, Mary, 149
Gene frequency, 118
Germany, population trend,
220, 223, 225, 226; children
in wartime, 230
Goldfish, mass protection, 53,
56, 68; effect of numbers on
growth rate, 92; on amount
of food taken, 136; on
learning, 159; leadership,
166; imitation, 170
Gross, A. O., 113
Group behavior, 22, 133;
stimulation of feeding, 136;
organization, 175
Growth, retarded by over-
crowding, 91; of goldfish,
effect of numbers, 92; ef-
fect of extracts on, 72, 96;
of mice, effect of numbers,
99
Gulls, minimal population,
110; effect of numbers on
survival, 111
Hawaii, snails, 123
Heath hen, 113, 122
Henry IV of France, 236
Hibernation, 32, 58
Holmes, S. J., 231
Hormones, effect on social
rank, 193; social, 264, 267
Hoskins, Walter, 92
Hunt, Harrison, 228
Imitation, 170
Insects, social, 26, 29, 32, 259;
population in nature, 39;
evolution of, 88; as enemies
of man, 241; castes, 250
Instinct, 249; definition, 246;
social, 244, 245, 249
International relations, 210
Isopods, behavior, 20
Italy, population trend, 219,
225, 226, 227; children in
wartime, 230
Japan, population, 226
Johnson, W. H., 77
Jordan, David Starr, 228
Kellogg, John, 185
Kessler, K. F., 26
Kropotkin, Prince, 27
Leader, of a group, 166, 175,
196, 207; relation to peck-
order, 199
League of Nations, 236
Learning, effect of numbers,
142
Liven good, Wayne, 92
Lobster-krills, 34
Locusts, migratory, 35; phases,
272
292
INDEX
Malinowski, B,, 213, 243
Man, 26; mass protection, 52,
85, 209; evolution of, 88;
effects of numbers on men-
tal work, 142; social rank-
ing, 201; war, 210; enemies
of, 240; castes, 251; com-
bativeness, 261
Manakin, breeding behavior,
134
Mass protection, 52, 85
Mast, S. O., 81
Masure, R., 185, 192
May-flies, 35
Maze learning, 150; relation
to social rank, 192
Metaphysics, 18
Mice, effect of numbers on
rate of growth, 99; on rate
of reproduction, 103
Migration, 33
Minnesota, experiments on
class size, 145
Mixed flocks, leadership in,
48, 197
Moina, sex determination,
257
Murchison, C, 182
Mutation, 118
Newman, H. H., 206
Netherlands, population, 226,
227
Nichols, J. T., 197
Paramecium, 76
Park, Thomas, 105
Parrakeet, effect of numbers
present on learning, 155;
social order, 185, 191, 192
Patten, W., 27
Pearl, Raymond, 107, 216,
218, 222, 223, 224
Peck-order, 176; relation to
leadership, 199
Phases of grasshoppers, 272
Phillips, John, 107
Philosophy, 17, 23
Pigeons, social order, 186, 207
Planaria, mass protection, 59
Poisons, mass protection from,
53' 56
Poland, children in wartime,
230
Popenoe and Johnson, 234
Population, optimal size, 92,
103, 104, 125, 128, 130, 131;
minimal, 108; human, re-
lation to war, 214; of the
world, 215, 218; of U. S. A.,
217; of various countries,
226
Procerodes, mass protection,
63
Protozoa, effect of numbers
on rate of division, 76; ex-
planation of effect, 80; as-
sociated with termites, 270
Pseudo-leadership, 197
Oesting, R. B., 92
Overcrowding, 31, 50; effect
on growth, 91, 103
Oxytricha, 77
Quintuplets, Dionne, 201, 207
Retzlaff, Elmer, 102
Robertson, T. B., 75
INDEX
293
Schjelderup-Ebbe, T., 176,
184, 185, 189, 191
Science in general, 15, 20, 90
Selection, 120, 125, 210, 228
Sex, 47; origin, 84; relation
to social dominance, 191,
194; division of labor, 247,
251
Shaftesbury, third Earl of, 24
Shaw, Gretchen, 92
Shoemaker, H. H., 185, 191,
193
Social, origins, 29, 244, 272,
274; inertia, 43, 44; appe-
tite, 44, 47; facilitation, 134,
172; hierarchy, 175, 207
Sociology, general, 200
Spermatozoa, mass protection,
68; length of life, 83
Springbok, 108
Starfish, brittle, 44
Statistical probability, 54
Struggle for existence, 26, 51,
210, 242
Sully, 236
Survival value, 32, 49, 133,
173, 244; of breeding col-
ony, 111; of social hier-
archy, 207
Tadpoles, effect of numbers
on regeneration, 98
Temperature, mass protec-
tion from, 58; effect on
growth of mice, 102
Termites, 32, 48, 261, 264,
265, 271
Territory, bird, 135; a factor
in social rank, 193
Toleration, 43, 44
Trial-and-error, 44
Tropism, 246. {See Forced
movements)
Tsetse fly, minimal popula-
tion, 108
Ultra-violet, mass protection
from, 59
Undercrowding, 50; harmful
effects, 52; effect on growth,
91
Vetulani, T., 99
War, 210
Wasps, 262, 264, 265; solitary,
46; importance of females,
259
Welty, J. C, 92, 136, 159
Wheeler, W. M:, 29, 40, 246,
259, 262, 264
Wheeling of bird flocks, 198
Wilder, Janet, 59
World Court, 238
Wright, Sewall, 117, 240